ast-utils.js

/**
 * @fileoverview Tests for ast utils.
 * @author Gyandeep Singh
 */

"use strict";

//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------

const assert = require("chai").assert,
    util = require("util"),
    espree = require("espree"),
    astUtils = require("../../../../lib/rules/utils/ast-utils"),
    { Linter } = require("../../../../lib/linter"),
    { SourceCode } = require("../../../../lib/source-code");

//------------------------------------------------------------------------------
// Tests
//------------------------------------------------------------------------------

const ESPREE_CONFIG = {
    ecmaVersion: 6,
    comment: true,
    tokens: true,
    range: true,
    loc: true
};
const linter = new Linter({ configType: "eslintrc" });

describe("ast-utils", () => {
    let callCounts;

    beforeEach(() => {
        callCounts = new Map();
    });

    /**
     * Asserts that a given function is called at least once during a test
     * @param {Function} func The function that must be called at least once
     * @returns {Function} A wrapper around the same function
     */
    function mustCall(func) {
        callCounts.set(func, 0);
        return function Wrapper(...args) {
            callCounts.set(func, callCounts.get(func) + 1);

            return func.call(this, ...args);
        };
    }

    afterEach(() => {
        callCounts.forEach((callCount, func) => {
            assert(
                callCount > 0,
                `Expected ${func.toString()} to be called at least once but it was not called`
            );
        });
    });

    describe("ECMASCRIPT_GLOBALS", () => {
        it("should contain es3 globals", () => {
            assert.ownInclude(astUtils.ECMASCRIPT_GLOBALS, { Object: false });
        });

        it("should contain es5 globals", () => {
            assert.ownInclude(astUtils.ECMASCRIPT_GLOBALS, { JSON: false });
        });

        it("should contain es2015 globals", () => {
            assert.ownInclude(astUtils.ECMASCRIPT_GLOBALS, { Promise: false });
        });

        it("should contain es2017 globals", () => {
            assert.ownInclude(astUtils.ECMASCRIPT_GLOBALS, { SharedArrayBuffer: false });
        });

        it("should contain es2020 globals", () => {
            assert.ownInclude(astUtils.ECMASCRIPT_GLOBALS, { BigInt: false });
        });

        it("should contain es2021 globals", () => {
            assert.ownInclude(astUtils.ECMASCRIPT_GLOBALS, { WeakRef: false });
        });
    });

    describe("isTokenOnSameLine", () => {
        it("should return false if the tokens are not on the same line", () => {
            linter.defineRule("checker", {
                create: mustCall(context => ({
                    BlockStatement: mustCall(node => {
                        assert.isFalse(astUtils.isTokenOnSameLine(context.sourceCode.getTokenBefore(node), node));
                    })
                }))
            });

            linter.verify("if(a)\n{}", { rules: { checker: "error" } });
        });

        it("should return true if the tokens are on the same line", () => {

            linter.defineRule("checker", {
                create: mustCall(context => ({
                    BlockStatement: mustCall(node => {
                        assert.isTrue(astUtils.isTokenOnSameLine(context.sourceCode.getTokenBefore(node), node));
                    })
                }))
            });

            linter.verify("if(a){}", { rules: { checker: "error" } });
        });
    });

    describe("isNullOrUndefined", () => {
        it("should return true if the argument is null", () => {
            assert.isTrue(astUtils.isNullOrUndefined(espree.parse("null").body[0].expression));
        });

        it("should return true if the argument is undefined", () => {
            assert.isTrue(astUtils.isNullOrUndefined(espree.parse("undefined").body[0].expression));
        });

        it("should return false if the argument is a number", () => {
            assert.isFalse(astUtils.isNullOrUndefined(espree.parse("1").body[0].expression));
        });

        it("should return false if the argument is a string", () => {
            assert.isFalse(astUtils.isNullOrUndefined(espree.parse("'test'").body[0].expression));
        });

        it("should return false if the argument is a boolean", () => {
            assert.isFalse(astUtils.isNullOrUndefined(espree.parse("true").body[0].expression));
        });

        it("should return false if the argument is an object", () => {
            assert.isFalse(astUtils.isNullOrUndefined(espree.parse("({})").body[0].expression));
        });

        it("should return false if the argument is a unicode regex", () => {
            assert.isFalse(astUtils.isNullOrUndefined(espree.parse("/abc/u", { ecmaVersion: 6 }).body[0].expression));
        });
    });

    describe("checkReference", () => {

        // catch
        it("should return true if reference is assigned for catch", () => {
            linter.defineRule("checker", {
                create: mustCall(context => ({
                    CatchClause: mustCall(node => {
                        const variables = context.sourceCode.getDeclaredVariables(node);

                        assert.lengthOf(astUtils.getModifyingReferences(variables[0].references), 1);
                    })
                }))
            });

            linter.verify("try { } catch (e) { e = 10; }", { rules: { checker: "error" } });
        });

        // const
        it("should return true if reference is assigned for const", () => {
            linter.defineRule("checker", {
                create: mustCall(context => ({
                    VariableDeclaration: mustCall(node => {
                        const variables = context.sourceCode.getDeclaredVariables(node);

                        assert.lengthOf(astUtils.getModifyingReferences(variables[0].references), 1);
                    })
                }))
            });

            linter.verify("const a = 1; a = 2;", { rules: { checker: "error" }, parserOptions: { ecmaVersion: 6 } });
        });

        it("should return false if reference is not assigned for const", () => {
            linter.defineRule("checker", {
                create: mustCall(context => ({
                    VariableDeclaration: mustCall(node => {
                        const variables = context.sourceCode.getDeclaredVariables(node);

                        assert.lengthOf(astUtils.getModifyingReferences(variables[0].references), 0);
                    })
                }))
            });

            linter.verify("const a = 1; c = 2;", { rules: { checker: "error" }, parserOptions: { ecmaVersion: 6 } });
        });

        // class
        it("should return true if reference is assigned for class", () => {
            linter.defineRule("checker", {
                create: mustCall(context => ({
                    ClassDeclaration: mustCall(node => {
                        const variables = context.sourceCode.getDeclaredVariables(node);

                        assert.lengthOf(astUtils.getModifyingReferences(variables[0].references), 1);
                        assert.lengthOf(astUtils.getModifyingReferences(variables[1].references), 0);
                    })
                }))
            });

            linter.verify("class A { }\n A = 1;", { rules: { checker: "error" }, parserOptions: { ecmaVersion: 6 } });
        });

        it("should return false if reference is not assigned for class", () => {
            linter.defineRule("checker", {
                create: mustCall(context => ({
                    ClassDeclaration: mustCall(node => {
                        const variables = context.sourceCode.getDeclaredVariables(node);

                        assert.lengthOf(astUtils.getModifyingReferences(variables[0].references), 0);
                    })
                }))
            });

            linter.verify("class A { } foo(A);", { rules: { checker: "error" }, parserOptions: { ecmaVersion: 6 } });
        });
    });

    describe("isDirectiveComment", () => {

        /**
         * Asserts the node is NOT a directive comment
         * @param {ASTNode} node node to assert
         * @returns {void}
         */
        function assertFalse(node) {
            assert.isFalse(astUtils.isDirectiveComment(node));
        }

        /**
         * Asserts the node is a directive comment
         * @param {ASTNode} node node to assert
         * @returns {void}
         */
        function assertTrue(node) {
            assert.isTrue(astUtils.isDirectiveComment(node));
        }

        it("should return false if it is not a directive line comment", () => {
            const code = [
                "// lalala I'm a normal comment",
                "// trying to confuse eslint ",
                "//trying to confuse eslint-directive-detection",
                "//eslint is awesome",
                "//global line comment is not a directive",
                "//globals line comment is not a directive",
                "//exported line comment is not a directive"
            ].join("\n");
            const ast = espree.parse(code, ESPREE_CONFIG);
            const sourceCode = new SourceCode(code, ast);
            const comments = sourceCode.getAllComments();

            comments.forEach(assertFalse);
        });

        it("should return false if it is not a directive block comment", () => {
            const code = [
                "/* lalala I'm a normal comment */",
                "/* trying to confuse eslint */",
                "/* trying to confuse eslint-directive-detection */",
                "/*eSlInT is awesome*/"
            ].join("\n");
            const ast = espree.parse(code, ESPREE_CONFIG);
            const sourceCode = new SourceCode(code, ast);
            const comments = sourceCode.getAllComments();

            comments.forEach(assertFalse);
        });

        it("should return true if it is a directive line comment", () => {
            const code = [
                "// eslint-disable-line no-undef",
                "// eslint-secret-directive 4 8 15 16 23 42   ",
                "// eslint-directive-without-argument",
                "//eslint-directive-without-padding"
            ].join("\n");
            const ast = espree.parse(code, ESPREE_CONFIG);
            const sourceCode = new SourceCode(code, ast);
            const comments = sourceCode.getAllComments();

            comments.forEach(assertTrue);
        });

        it("should return true if it is a directive block comment", () => {
            const code = [
                "/* eslint-disable no-undef */",
                "/*eslint-enable no-undef*/",
                "/* eslint-env {\"es6\": true} */",
                "/* eslint foo */",
                "/*eslint bar*/",
                "/*global foo*/",
                "/*globals foo*/",
                "/*exported foo*/"
            ].join("\n");
            const ast = espree.parse(code, ESPREE_CONFIG);
            const sourceCode = new SourceCode(code, ast);
            const comments = sourceCode.getAllComments();

            comments.forEach(assertTrue);
        });
    });

    describe("isParenthesised", () => {
        it("should return false for not parenthesised nodes", () => {
            const code = "condition ? 1 : 2";
            const ast = espree.parse(code, ESPREE_CONFIG);
            const sourceCode = new SourceCode(code, ast);

            assert.isFalse(astUtils.isParenthesised(sourceCode, ast.body[0].expression));
        });

        it("should return true for not parenthesised nodes", () => {
            const code = "(condition ? 1 : 2)";
            const ast = espree.parse(code, ESPREE_CONFIG);
            const sourceCode = new SourceCode(code, ast);

            assert.isTrue(astUtils.isParenthesised(sourceCode, ast.body[0].expression));
        });
    });

    describe("isFunction", () => {
        it("should return true for FunctionDeclaration", () => {
            const ast = espree.parse("function a() {}");
            const node = ast.body[0];

            assert(astUtils.isFunction(node));
        });

        it("should return true for FunctionExpression", () => {
            const ast = espree.parse("(function a() {})");
            const node = ast.body[0].expression;

            assert(astUtils.isFunction(node));
        });

        it("should return true for AllowFunctionExpression", () => {
            const ast = espree.parse("(() => {})", { ecmaVersion: 6 });
            const node = ast.body[0].expression;

            assert(astUtils.isFunction(node));
        });

        it("should return false for Program, VariableDeclaration, BlockStatement", () => {
            const ast = espree.parse("var a; { }");

            assert(!astUtils.isFunction(ast));
            assert(!astUtils.isFunction(ast.body[0]));
            assert(!astUtils.isFunction(ast.body[1]));
        });
    });

    describe("isLoop", () => {
        it("should return true for DoWhileStatement", () => {
            const ast = espree.parse("do {} while (a)");
            const node = ast.body[0];

            assert(astUtils.isLoop(node));
        });

        it("should return true for ForInStatement", () => {
            const ast = espree.parse("for (var k in obj) {}");
            const node = ast.body[0];

            assert(astUtils.isLoop(node));
        });

        it("should return true for ForOfStatement", () => {
            const ast = espree.parse("for (var x of list) {}", { ecmaVersion: 6 });
            const node = ast.body[0];

            assert(astUtils.isLoop(node));
        });

        it("should return true for ForStatement", () => {
            const ast = espree.parse("for (var i = 0; i < 10; ++i) {}");
            const node = ast.body[0];

            assert(astUtils.isLoop(node));
        });

        it("should return true for WhileStatement", () => {
            const ast = espree.parse("while (a) {}");
            const node = ast.body[0];

            assert(astUtils.isLoop(node));
        });

        it("should return false for Program, VariableDeclaration, BlockStatement", () => {
            const ast = espree.parse("var a; { }");

            assert(!astUtils.isLoop(ast));
            assert(!astUtils.isLoop(ast.body[0]));
            assert(!astUtils.isLoop(ast.body[1]));
        });
    });

    describe("isInLoop", () => {

        /**
         * Asserts that the unique node of the given type in the code is either
         * in a loop or not in a loop.
         * @param {string} code the code to check.
         * @param {string} nodeType the type of the node to consider. The code
         *      must have exactly one node of ths type.
         * @param {boolean} expectedInLoop the expected result for whether the
         *      node is in a loop.
         * @returns {void}
         */
        function assertNodeTypeInLoop(code, nodeType, expectedInLoop) {
            const results = [];

            linter.defineRule("checker", {
                create: mustCall(() => ({
                    [nodeType]: mustCall(node => {
                        results.push(astUtils.isInLoop(node));
                    })
                }))
            });
            linter.verify(code, { rules: { checker: "error" }, parserOptions: { ecmaVersion: 6 } });

            assert.lengthOf(results, 1);
            assert.strictEqual(results[0], expectedInLoop);
        }

        it("should return true for a loop itself", () => {
            assertNodeTypeInLoop("while (a) {}", "WhileStatement", true);
        });

        it("should return true for a loop condition", () => {
            assertNodeTypeInLoop("while (a) {}", "Identifier", true);
        });

        it("should return true for a loop assignee", () => {
            assertNodeTypeInLoop("for (var a in b) {}", "VariableDeclaration", true);
        });

        it("should return true for a node within a loop body", () => {
            assertNodeTypeInLoop("for (var a of b) { console.log('Hello'); }", "Literal", true);
        });

        it("should return false for a node outside a loop body", () => {
            assertNodeTypeInLoop("while (true) {} a(b);", "CallExpression", false);
        });

        it("should return false when the loop is not in the current function", () => {
            assertNodeTypeInLoop("while (true) { funcs.push(() => { var a; }); }", "VariableDeclaration", false);
        });
    });

    describe("getStaticStringValue", () => {

        /* eslint-disable quote-props -- Make consistent here for readability */
        const expectedResults = {

            // string literals
            "''": "",
            "'foo'": "foo",

            // boolean literals
            "false": "false",
            "true": "true",

            // null literal
            "null": "null",

            // number literals
            "0": "0",
            "0.": "0",
            ".0": "0",
            "1": "1",
            "1.": "1",
            ".1": "0.1",
            "12": "12",
            ".12": "0.12",
            "0.12": "0.12",
            "12.34": "12.34",
            "12e3": "12000",
            "12e-3": "0.012",
            "12.34e5": "1234000",
            "12.34e-5": "0.0001234",
            "011": "9",
            "081": "81",
            "0b11": "3",
            "0b011": "3",
            "0o11": "9",
            "0o011": "9",
            "0x11": "17",
            "0x011": "17",

            // regexp literals
            "/a/": "/a/",
            "/a/i": "/a/i",
            "/[0-9]/": "/[0-9]/",
            "/(?<zero>0)/": "/(?<zero>0)/",
            "/(?<zero>0)/s": "/(?<zero>0)/s",
            "/(?<=a)b/s": "/(?<=a)b/s",

            // simple template literals
            "``": "",
            "`foo`": "foo",

            // unsupported
            "`${''}`": null,
            "`${0}`": null,
            "tag``": null,
            "-0": null,
            "-1": null,
            "1 + 2": null,
            "[]": null,
            "({})": null,
            "foo": null,
            "undefined": null,
            "this": null,
            "(function () {})": null
        };
        /* eslint-enable quote-props -- Make consistent here for readability */

        Object.keys(expectedResults).forEach(key => {
            it(`should return ${expectedResults[key]} for ${key}`, () => {
                const ast = espree.parse(key, { ecmaVersion: 2018 });

                assert.strictEqual(astUtils.getStaticStringValue(ast.body[0].expression), expectedResults[key]);
            });
        });

        it("should return text of regex literal even if it's not supported natively.", () => {
            const node = {
                type: "Literal",
                value: null,
                regex: { pattern: "(?:)", flags: "u" }
            };
            const expectedText = "/(?:)/u";

            assert.strictEqual(astUtils.getStaticStringValue(node), expectedText);
        });

        it("should return text of bigint literal even if it's not supported natively.", () => {
            const node = {
                type: "Literal",
                value: null,
                bigint: "100n"
            };
            const expectedText = "100n";

            assert.strictEqual(astUtils.getStaticStringValue(node), expectedText);
        });
    });

    describe("getStaticPropertyName", () => {
        it("should return 'b' for `a.b`", () => {
            const ast = espree.parse("a.b");
            const node = ast.body[0].expression;

            assert.strictEqual(astUtils.getStaticPropertyName(node), "b");
        });

        it("should return 'b' for `a['b']`", () => {
            const ast = espree.parse("a['b']");
            const node = ast.body[0].expression;

            assert.strictEqual(astUtils.getStaticPropertyName(node), "b");
        });

        it("should return 'b' for `a[`b`]`", () => {
            const ast = espree.parse("a[`b`]", { ecmaVersion: 6 });
            const node = ast.body[0].expression;

            assert.strictEqual(astUtils.getStaticPropertyName(node), "b");
        });

        it("should return '100' for `a[100]`", () => {
            const ast = espree.parse("a[100]");
            const node = ast.body[0].expression;

            assert.strictEqual(astUtils.getStaticPropertyName(node), "100");
        });

        it("should return null for `a[b]`", () => {
            const ast = espree.parse("a[b]");
            const node = ast.body[0].expression;

            assert.strictEqual(astUtils.getStaticPropertyName(node), null);
        });

        it("should return null for `a['a' + 'b']`", () => {
            const ast = espree.parse("a['a' + 'b']");
            const node = ast.body[0].expression;

            assert.strictEqual(astUtils.getStaticPropertyName(node), null);
        });

        it("should return null for `a[tag`b`]`", () => {
            const ast = espree.parse("a[tag`b`]", { ecmaVersion: 6 });
            const node = ast.body[0].expression;

            assert.strictEqual(astUtils.getStaticPropertyName(node), null);
        });

        it("should return null for `a[`${b}`]`", () => {
            const ast = espree.parse("a[`${b}`]", { ecmaVersion: 6 });
            const node = ast.body[0].expression;

            assert.strictEqual(astUtils.getStaticPropertyName(node), null);
        });

        it("should return 'b' for `b: 1`", () => {
            const ast = espree.parse("({b: 1})");
            const node = ast.body[0].expression.properties[0];

            assert.strictEqual(astUtils.getStaticPropertyName(node), "b");
        });

        it("should return 'b' for `b() {}`", () => {
            const ast = espree.parse("({b() {}})", { ecmaVersion: 6 });
            const node = ast.body[0].expression.properties[0];

            assert.strictEqual(astUtils.getStaticPropertyName(node), "b");
        });

        it("should return 'b' for `get b() {}`", () => {
            const ast = espree.parse("({get b() {}})", { ecmaVersion: 6 });
            const node = ast.body[0].expression.properties[0];

            assert.strictEqual(astUtils.getStaticPropertyName(node), "b");
        });

        it("should return 'b' for `['b']: 1`", () => {
            const ast = espree.parse("({['b']: 1})", { ecmaVersion: 6 });
            const node = ast.body[0].expression.properties[0];

            assert.strictEqual(astUtils.getStaticPropertyName(node), "b");
        });

        it("should return 'b' for `['b']() {}`", () => {
            const ast = espree.parse("({['b']() {}})", { ecmaVersion: 6 });
            const node = ast.body[0].expression.properties[0];

            assert.strictEqual(astUtils.getStaticPropertyName(node), "b");
        });

        it("should return 'b' for `[`b`]: 1`", () => {
            const ast = espree.parse("({[`b`]: 1})", { ecmaVersion: 6 });
            const node = ast.body[0].expression.properties[0];

            assert.strictEqual(astUtils.getStaticPropertyName(node), "b");
        });

        it("should return '100' for` [100]: 1`", () => {
            const ast = espree.parse("({[100]: 1})", { ecmaVersion: 6 });
            const node = ast.body[0].expression.properties[0];

            assert.strictEqual(astUtils.getStaticPropertyName(node), "100");
        });

        it("should return '/(?<zero>0)/' for `[/(?<zero>0)/]: 1`", () => {
            const ast = espree.parse("({[/(?<zero>0)/]: 1})", { ecmaVersion: 2018 });
            const node = ast.body[0].expression.properties[0];

            assert.strictEqual(astUtils.getStaticPropertyName(node), "/(?<zero>0)/");
        });

        it("should return null for `[b]: 1`", () => {
            const ast = espree.parse("({[b]: 1})", { ecmaVersion: 6 });
            const node = ast.body[0].expression.properties[0];

            assert.strictEqual(astUtils.getStaticPropertyName(node), null);
        });

        it("should return null for `['a' + 'b']: 1`", () => {
            const ast = espree.parse("({['a' + 'b']: 1})", { ecmaVersion: 6 });
            const node = ast.body[0].expression.properties[0];

            assert.strictEqual(astUtils.getStaticPropertyName(node), null);
        });

        it("should return null for `[tag`b`]: 1`", () => {
            const ast = espree.parse("({[tag`b`]: 1})", { ecmaVersion: 6 });
            const node = ast.body[0].expression.properties[0];

            assert.strictEqual(astUtils.getStaticPropertyName(node), null);
        });

        it("should return null for `[`${b}`]: 1`", () => {
            const ast = espree.parse("({[`${b}`]: 1})", { ecmaVersion: 6 });
            const node = ast.body[0].expression.properties[0];

            assert.strictEqual(astUtils.getStaticPropertyName(node), null);
        });

        it("should return null for non member expressions", () => {
            const ast = espree.parse("foo()");

            assert.strictEqual(astUtils.getStaticPropertyName(ast.body[0].expression), null);
            assert.strictEqual(astUtils.getStaticPropertyName(ast.body[0]), null);
            assert.strictEqual(astUtils.getStaticPropertyName(ast.body), null);
            assert.strictEqual(astUtils.getStaticPropertyName(ast), null);
            assert.strictEqual(astUtils.getStaticPropertyName(null), null);
        });
    });

    describe("getDirectivePrologue", () => {
        it("should return empty array if node is not a Program, FunctionDeclaration, FunctionExpression, or ArrowFunctionExpression", () => {
            const ast = espree.parse("if (a) { b(); }");
            const node = ast.body[0];

            assert.deepStrictEqual(astUtils.getDirectivePrologue(node), []);
        });

        it("should return empty array if node is a braceless ArrowFunctionExpression node", () => {
            const ast = espree.parse("var foo = () => 'use strict';", { ecmaVersion: 6 });
            const node = ast.body[0].declarations[0].init;

            assert.deepStrictEqual(astUtils.getDirectivePrologue(node), []);
        });

        it("should return empty array if there are no directives in Program body", () => {
            const ast = espree.parse("var foo;");
            const node = ast;

            assert.deepStrictEqual(astUtils.getDirectivePrologue(node), []);
        });

        it("should return empty array if there are no directives in FunctionDeclaration body", () => {
            const ast = espree.parse("function foo() { return bar; }");
            const node = ast.body[0];

            assert.deepStrictEqual(astUtils.getDirectivePrologue(node), []);
        });

        it("should return empty array if there are no directives in FunctionExpression body", () => {
            const ast = espree.parse("var foo = function() { return bar; }");
            const node = ast.body[0].declarations[0].init;

            assert.deepStrictEqual(astUtils.getDirectivePrologue(node), []);
        });

        it("should return empty array if there are no directives in ArrowFunctionExpression body", () => {
            const ast = espree.parse("var foo = () => { return bar; };", { ecmaVersion: 6 });
            const node = ast.body[0].declarations[0].init;

            assert.deepStrictEqual(astUtils.getDirectivePrologue(node), []);
        });

        it("should return directives in Program body", () => {
            const ast = espree.parse("'use strict'; 'use asm'; var foo;");
            const result = astUtils.getDirectivePrologue(ast);

            assert.strictEqual(result.length, 2);
            assert.strictEqual(result[0].expression.value, "use strict");
            assert.strictEqual(result[1].expression.value, "use asm");
        });

        it("should return directives in FunctionDeclaration body", () => {
            const ast = espree.parse("function foo() { 'use strict'; 'use asm'; return bar; }");
            const result = astUtils.getDirectivePrologue(ast.body[0]);

            assert.strictEqual(result.length, 2);
            assert.strictEqual(result[0].expression.value, "use strict");
            assert.strictEqual(result[1].expression.value, "use asm");
        });

        it("should return directives in FunctionExpression body", () => {
            const ast = espree.parse("var foo = function() { 'use strict'; 'use asm'; return bar; }");
            const result = astUtils.getDirectivePrologue(ast.body[0].declarations[0].init);

            assert.strictEqual(result.length, 2);
            assert.strictEqual(result[0].expression.value, "use strict");
            assert.strictEqual(result[1].expression.value, "use asm");
        });

        it("should return directives in ArrowFunctionExpression body", () => {
            const ast = espree.parse("var foo = () => { 'use strict'; 'use asm'; return bar; };", { ecmaVersion: 6 });
            const result = astUtils.getDirectivePrologue(ast.body[0].declarations[0].init);

            assert.strictEqual(result.length, 2);
            assert.strictEqual(result[0].expression.value, "use strict");
            assert.strictEqual(result[1].expression.value, "use asm");
        });
    });

    {
        const expectedResults = {
            0: true,
            5: true,
            8: true,
            9: true,
            50: true,
            123: true,
            "1_0": true,
            "1_0_1": true,
            "12_3": true,
            "5_000": true,
            "500_0": true,
            "500_00": true,
            "5_000_00": true,
            "1_234_56": true,
            "1_2_3_4": true,
            "11_22_33_44": true,
            "1_23_4_56_7_89": true,
            "08": true,
            "09": true,
            "008": true,
            "0192": true,
            "0180": true,
            "090": true,
            "088": true,
            "099": true,
            "089": true,
            "0098": true,
            "01892": true,
            "08192": true,
            "01829": true,
            "018290": true,
            "0.": false,
            "5.": false,
            ".0": false,
            ".5": false,
            "5.0": false,
            "5.00_00": false,
            "5.0_1": false,
            "0.1_0": false,
            "5.1_2": false,
            "1.23_45": false,
            ".0_1": false,
            ".12_34": false,
            "05": false,
            "0123": false,
            "076543210": false,
            "08.": false,
            "0x5": false,
            "0b11_01": false,
            "0o0_1": false,
            "0x56_78": false,
            "5e0": false,
            "0.e1": false,
            ".0e1": false,
            "5e0_1": false,
            "5e1_000": false,
            "5e12_34": false,
            "5e-0": false,
            "5e-0_1": false,
            "5e-1_2": false,
            "1_2.3_4e5_6": false,
            "1n": false,
            "1_2n": false,
            "1_000n": false,
            "'5'": false
        };

        const ecmaVersion = espree.latestEcmaVersion;

        describe("isDecimalInteger", () => {
            Object.keys(expectedResults).forEach(key => {
                it(`should return ${expectedResults[key]} for ${key}`, () => {
                    assert.strictEqual(
                        astUtils.isDecimalInteger(
                            espree.parse(key, { ecmaVersion }).body[0].expression
                        ),
                        expectedResults[key]
                    );
                });
            });
        });

        describe("isDecimalIntegerNumericToken", () => {
            Object.keys(expectedResults).forEach(key => {
                it(`should return ${expectedResults[key]} for ${key}`, () => {
                    assert.strictEqual(
                        astUtils.isDecimalIntegerNumericToken(
                            espree.tokenize(key, { ecmaVersion })[0]
                        ),
                        expectedResults[key]
                    );
                });
            });
        });
    }

    describe("getFunctionNameWithKind", () => {
        const expectedResults = {
            "function foo() {}": "function 'foo'",
            "(function foo() {})": "function 'foo'",
            "(function() {})": "function",
            "function* foo() {}": "generator function 'foo'",
            "(function* foo() {})": "generator function 'foo'",
            "(function*() {})": "generator function",
            "() => {}": "arrow function",
            "async () => {}": "async arrow function",
            "({ foo: function foo() {} })": "method 'foo'",
            "({ foo: function() {} })": "method 'foo'",
            "({ '': function() {} })": "method ''",
            "({ ['foo']: function() {} })": "method 'foo'",
            "({ ['']: function() {} })": "method ''",
            "({ [foo]: function() {} })": "method",
            "({ foo() {} })": "method 'foo'",
            "({ foo: function* foo() {} })": "generator method 'foo'",
            "({ foo: function*() {} })": "generator method 'foo'",
            "({ ['foo']: function*() {} })": "generator method 'foo'",
            "({ [foo]: function*() {} })": "generator method",
            "({ *foo() {} })": "generator method 'foo'",
            "({ foo: async function foo() {} })": "async method 'foo'",
            "({ foo: async function() {} })": "async method 'foo'",
            "({ ['foo']: async function() {} })": "async method 'foo'",
            "({ [foo]: async function() {} })": "async method",
            "({ async foo() {} })": "async method 'foo'",
            "({ get foo() {} })": "getter 'foo'",
            "({ set foo(a) {} })": "setter 'foo'",
            "class A { constructor() {} }": "constructor",
            "class A { foo() {} }": "method 'foo'",
            "class A { *foo() {} }": "generator method 'foo'",
            "class A { async foo() {} }": "async method 'foo'",
            "class A { ['foo']() {} }": "method 'foo'",
            "class A { *['foo']() {} }": "generator method 'foo'",
            "class A { async ['foo']() {} }": "async method 'foo'",
            "class A { [foo]() {} }": "method",
            "class A { *[foo]() {} }": "generator method",
            "class A { async [foo]() {} }": "async method",
            "class A { get foo() {} }": "getter 'foo'",
            "class A { set foo(a) {} }": "setter 'foo'",
            "class A { static foo() {} }": "static method 'foo'",
            "class A { static *foo() {} }": "static generator method 'foo'",
            "class A { static async foo() {} }": "static async method 'foo'",
            "class A { static get foo() {} }": "static getter 'foo'",
            "class A { static set foo(a) {} }": "static setter 'foo'",
            "class A { foo = () => {}; }": "method 'foo'",
            "class A { foo = function() {}; }": "method 'foo'",
            "class A { foo = function bar() {}; }": "method 'foo'",
            "class A { static foo = () => {}; }": "static method 'foo'",
            "class A { '#foo' = () => {}; }": "method '#foo'",
            "class A { #foo = () => {}; }": "private method #foo",
            "class A { static #foo = () => {}; }": "static private method #foo",
            "class A { '#foo'() {} }": "method '#foo'",
            "class A { #foo() {} }": "private method #foo",
            "class A { static #foo() {} }": "static private method #foo"
        };

        Object.keys(expectedResults).forEach(key => {
            it(`should return "${expectedResults[key]}" for "${key}".`, () => {
                linter.defineRule("checker", {
                    create: mustCall(() => ({
                        ":function": mustCall(node => {
                            assert.strictEqual(
                                astUtils.getFunctionNameWithKind(node),
                                expectedResults[key]
                            );
                        })
                    }))
                });

                linter.verify(key, { rules: { checker: "error" }, parserOptions: { ecmaVersion: 13 } });
            });
        });
    });

    describe("getFunctionHeadLoc", () => {
        const expectedResults = {
            "function foo() {}": [0, 12],
            "(function foo() {})": [1, 13],
            "(function() {})": [1, 9],
            "function* foo() {}": [0, 13],
            "(function* foo() {})": [1, 14],
            "(function*() {})": [1, 10],
            "() => {}": [3, 5],
            "async () => {}": [9, 11],
            "({ foo: function foo() {} })": [3, 20],
            "({ foo: function() {} })": [3, 16],
            "({ ['foo']: function() {} })": [3, 20],
            "({ [foo]: function() {} })": [3, 18],
            "({ foo() {} })": [3, 6],
            "({ foo: function* foo() {} })": [3, 21],
            "({ foo: function*() {} })": [3, 17],
            "({ ['foo']: function*() {} })": [3, 21],
            "({ [foo]: function*() {} })": [3, 19],
            "({ *foo() {} })": [3, 7],
            "({ foo: async function foo() {} })": [3, 26],
            "({ foo: async function() {} })": [3, 22],
            "({ ['foo']: async function() {} })": [3, 26],
            "({ [foo]: async function() {} })": [3, 24],
            "({ async foo() {} })": [3, 12],
            "({ get foo() {} })": [3, 10],
            "({ set foo(a) {} })": [3, 10],
            "class A { constructor() {} }": [10, 21],
            "class A { foo() {} }": [10, 13],
            "class A { *foo() {} }": [10, 14],
            "class A { async foo() {} }": [10, 19],
            "class A { ['foo']() {} }": [10, 17],
            "class A { *['foo']() {} }": [10, 18],
            "class A { async ['foo']() {} }": [10, 23],
            "class A { [foo]() {} }": [10, 15],
            "class A { *[foo]() {} }": [10, 16],
            "class A { async [foo]() {} }": [10, 21],
            "class A { get foo() {} }": [10, 17],
            "class A { set foo(a) {} }": [10, 17],
            "class A { static foo() {} }": [10, 20],
            "class A { static *foo() {} }": [10, 21],
            "class A { static async foo() {} }": [10, 26],
            "class A { static get foo() {} }": [10, 24],
            "class A { static set foo(a) {} }": [10, 24],
            "class A { foo = function() {}; }": [10, 24],
            "class A { foo = function bar() {}; }": [10, 28],
            "class A { static foo = function() {}; }": [10, 31],
            "class A { foo = () => {}; }": [10, 16],
            "class A { foo = arg => {}; }": [10, 16]
        };

        Object.keys(expectedResults).forEach(key => {
            const expectedLoc = {
                start: {
                    line: 1,
                    column: expectedResults[key][0]
                },
                end: {
                    line: 1,
                    column: expectedResults[key][1]
                }
            };

            it(`should return "${JSON.stringify(expectedLoc)}" for "${key}".`, () => {
                linter.defineRule("checker", {
                    create: mustCall(() => ({
                        ":function": mustCall(node => {
                            assert.deepStrictEqual(
                                astUtils.getFunctionHeadLoc(node, linter.getSourceCode()),
                                expectedLoc
                            );
                        })
                    }))
                });

                linter.verify(key, { rules: { checker: "error" }, parserOptions: { ecmaVersion: 13 } }, "test.js", true);
            });
        });
    });

    describe("isEmptyBlock", () => {
        const expectedResults = {
            "{}": true,
            "{ a }": false,
            a: false
        };

        Object.keys(expectedResults).forEach(key => {
            it(`should return ${expectedResults[key]} for ${key}`, () => {
                const ast = espree.parse(key);

                assert.strictEqual(astUtils.isEmptyBlock(ast.body[0]), expectedResults[key]);
            });
        });
    });

    describe("isEmptyFunction", () => {
        const expectedResults = {
            "(function foo() {})": true,
            "(function foo() { a })": false,
            "(a) => {}": true,
            "(a) => { a }": false,
            "(a) => a": false
        };

        Object.keys(expectedResults).forEach(key => {
            it(`should return ${expectedResults[key]} for ${key}`, () => {
                const ast = espree.parse(key, { ecmaVersion: 6 });

                assert.strictEqual(astUtils.isEmptyFunction(ast.body[0].expression), expectedResults[key]);
            });
        });
    });

    describe("getNextLocation", () => {

        /* eslint-disable quote-props -- Make consistent here for readability */
        const expectedResults = {
            "": [[1, 0], null],
            "\n": [[1, 0], [2, 0], null],
            "\r\n": [[1, 0], [2, 0], null],
            "foo": [[1, 0], [1, 1], [1, 2], [1, 3], null],
            "foo\n": [[1, 0], [1, 1], [1, 2], [1, 3], [2, 0], null],
            "foo\r\n": [[1, 0], [1, 1], [1, 2], [1, 3], [2, 0], null],
            "foo;\n": [[1, 0], [1, 1], [1, 2], [1, 3], [1, 4], [2, 0], null],
            "a\nb": [[1, 0], [1, 1], [2, 0], [2, 1], null],
            "a\nb\n": [[1, 0], [1, 1], [2, 0], [2, 1], [3, 0], null],
            "a\r\nb\r\n": [[1, 0], [1, 1], [2, 0], [2, 1], [3, 0], null],
            "a\nb\r\n": [[1, 0], [1, 1], [2, 0], [2, 1], [3, 0], null],
            "a\n\n": [[1, 0], [1, 1], [2, 0], [3, 0], null],
            "a\r\n\r\n": [[1, 0], [1, 1], [2, 0], [3, 0], null],
            "\n\r\n\n\r\n": [[1, 0], [2, 0], [3, 0], [4, 0], [5, 0], null],
            "ab\u2029c": [[1, 0], [1, 1], [1, 2], [2, 0], [2, 1], null],
            "ab\ncde\n": [[1, 0], [1, 1], [1, 2], [2, 0], [2, 1], [2, 2], [2, 3], [3, 0], null],
            "a ": [[1, 0], [1, 1], [1, 2], null],
            "a\t": [[1, 0], [1, 1], [1, 2], null],
            "a \n": [[1, 0], [1, 1], [1, 2], [2, 0], null]
        };
        /* eslint-enable quote-props -- Make consistent here for readability */

        Object.keys(expectedResults).forEach(code => {
            it(`should return expected locations for "${code}".`, () => {
                const ast = espree.parse(code, ESPREE_CONFIG);
                const sourceCode = new SourceCode(code, ast);
                const locations = expectedResults[code];

                for (let i = 0; i < locations.length - 1; i++) {
                    const location = { line: locations[i][0], column: locations[i][1] };
                    const expectedNextLocation = locations[i + 1]
                        ? { line: locations[i + 1][0], column: locations[i + 1][1] }
                        : null;

                    assert.deepStrictEqual(
                        astUtils.getNextLocation(sourceCode, location),
                        expectedNextLocation
                    );
                }
            });
        });
    });

    describe("getParenthesisedText", () => {
        const expectedResults = {
            "(((foo))); bar;": "(((foo)))",
            "(/* comment */(((foo.bar())))); baz();": "(/* comment */(((foo.bar()))))",
            "(foo, bar)": "(foo, bar)"
        };

        Object.keys(expectedResults).forEach(key => {
            it(`should return ${expectedResults[key]} for ${key}`, () => {
                const ast = espree.parse(key, { tokens: true, comment: true, range: true, loc: true });
                const sourceCode = new SourceCode(key, ast);

                assert.strictEqual(astUtils.getParenthesisedText(sourceCode, ast.body[0].expression), expectedResults[key]);
            });
        });
    });

    describe("couldBeError", () => {
        const EXPECTED_RESULTS = {
            5: false,
            null: false,
            true: false,
            "'foo'": false,
            "`foo`": false,
            foo: true,
            "new Foo": true,
            "Foo()": true,
            "foo`bar`": true,
            "foo.bar": true,
            "(foo = bar)": true,
            "(foo = 1)": false,
            "(foo += bar)": false,
            "(foo -= bar)": false,
            "(foo *= bar)": false,
            "(foo /= bar)": false,
            "(foo %= bar)": false,
            "(foo **= bar)": false,
            "(foo <<= bar)": false,
            "(foo >>= bar)": false,
            "(foo >>>= bar)": false,
            "(foo &= bar)": false,
            "(foo |= bar)": false,
            "(foo ^= bar)": false,
            "(1, 2, 3)": false,
            "(foo, 2, 3)": false,
            "(1, 2, foo)": true,
            "1 && 2": false,
            "1 && foo": true,
            "foo && 2": false,

            // A future improvement could detect the left side as statically falsy, making this false.
            "false && foo": true,
            "foo &&= 2": false,
            "foo.bar ??= 2": true,
            "foo[bar] ||= 2": true,
            "foo ? 1 : 2": false,
            "foo ? bar : 2": true,
            "foo ? 1 : bar": true,
            "[1, 2, 3]": false,
            "({ foo: 1 })": false
        };

        Object.keys(EXPECTED_RESULTS).forEach(key => {
            it(`returns ${EXPECTED_RESULTS[key]} for ${key}`, () => {
                const ast = espree.parse(key, { ecmaVersion: 2021 });

                assert.strictEqual(astUtils.couldBeError(ast.body[0].expression), EXPECTED_RESULTS[key]);
            });
        });
    });

    describe("isArrowToken", () => {
        const code = "() => 5";
        const tokens = espree.parse(code, { ecmaVersion: 6, tokens: true }).tokens;
        const expected = [false, false, true, false];

        tokens.forEach((token, index) => {
            it(`should return ${expected[index]} for '${token.value}'.`, () => {
                assert.strictEqual(astUtils.isArrowToken(token), expected[index]);
            });
        });
    });

    {
        const code = "if (obj && foo) { obj[foo](); }";
        const tokens = espree.parse(code, { ecmaVersion: 6, tokens: true }).tokens;
        const expected = [false, false, false, false, false, false, false, false, false, false, false, false, false, false, true];

        describe("isClosingBraceToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isClosingBraceToken(token), expected[index]);
                });
            });
        });

        describe("isNotClosingBraceToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isNotClosingBraceToken(token), !expected[index]);
                });
            });
        });
    }

    {
        const code = "if (obj && foo) { obj[foo](); }";
        const tokens = espree.parse(code, { ecmaVersion: 6, tokens: true }).tokens;
        const expected = [false, false, false, false, false, false, false, false, false, false, true, false, false, false, false];

        describe("isClosingBracketToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isClosingBracketToken(token), expected[index]);
                });
            });
        });

        describe("isNotClosingBracketToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isNotClosingBracketToken(token), !expected[index]);
                });
            });
        });
    }

    {
        const code = "if (obj && foo) { obj[foo](); }";
        const tokens = espree.parse(code, { ecmaVersion: 6, tokens: true }).tokens;
        const expected = [false, false, false, false, false, true, false, false, false, false, false, false, true, false, false];

        describe("isClosingParenToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isClosingParenToken(token), expected[index]);
                });
            });
        });

        describe("isNotClosingParenToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isNotClosingParenToken(token), !expected[index]);
                });
            });
        });
    }

    {
        const code = "const obj = {foo: 1, bar: 2};";
        const tokens = espree.parse(code, { ecmaVersion: 6, tokens: true }).tokens;
        const expected = [false, false, false, false, false, true, false, false, false, true, false, false, false];

        describe("isColonToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isColonToken(token), expected[index]);
                });
            });
        });

        describe("isNotColonToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isNotColonToken(token), !expected[index]);
                });
            });
        });
    }

    {
        const code = "const obj = {foo: 1, bar: 2};";
        const tokens = espree.parse(code, { ecmaVersion: 6, tokens: true }).tokens;
        const expected = [false, false, false, false, false, false, false, true, false, false, false, false, false];

        describe("isCommaToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isCommaToken(token), expected[index]);
                });
            });
        });

        describe("isNotCommaToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isNotCommaToken(token), !expected[index]);
                });
            });
        });
    }

    {
        const code = "const obj = {foo: 1.5, bar: a.b};";
        const tokens = espree.parse(code, { ecmaVersion: 6, tokens: true }).tokens;
        const expected = [false, false, false, false, false, false, false, false, false, false, false, true, false, false, false];

        describe("isDotToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isDotToken(token), expected[index]);
                });
            });
        });

        describe("isNotDotToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${!expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isNotDotToken(token), !expected[index]);
                });
            });
        });
    }

    describe("isCommentToken", () => {
        const code = "const obj = /*block*/ {foo: 1, bar: 2}; //line";
        const ast = espree.parse(code, { ecmaVersion: 6, tokens: true, comment: true });

        ast.tokens.forEach(token => {
            it(`should return false for '${token.value}'.`, () => {
                assert.strictEqual(astUtils.isCommentToken(token), false);
            });
        });
        ast.comments.forEach(comment => {
            it(`should return true for '${comment.value}'.`, () => {
                assert.strictEqual(astUtils.isCommentToken(comment), true);
            });
        });
    });

    describe("isKeywordToken", () => {
        const code = "const obj = {foo: 1, bar: 2};";
        const tokens = espree.parse(code, { ecmaVersion: 6, tokens: true }).tokens;
        const expected = [true, false, false, false, false, false, false, false, false, false, false, false, false];

        tokens.forEach((token, index) => {
            it(`should return ${expected[index]} for '${token.value}'.`, () => {
                assert.strictEqual(astUtils.isKeywordToken(token), expected[index]);
            });
        });
    });

    {
        const code = "if (obj && foo) { obj[foo](); }";
        const tokens = espree.parse(code, { ecmaVersion: 6, tokens: true }).tokens;
        const expected = [false, false, false, false, false, false, true, false, false, false, false, false, false, false, false];

        describe("isOpeningBraceToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isOpeningBraceToken(token), expected[index]);
                });
            });
        });

        describe("isNotOpeningBraceToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isNotOpeningBraceToken(token), !expected[index]);
                });
            });
        });
    }

    {
        const code = "if (obj && foo) { obj[foo](); }";
        const tokens = espree.parse(code, { ecmaVersion: 6, tokens: true }).tokens;
        const expected = [false, false, false, false, false, false, false, false, true, false, false, false, false, false, false];

        describe("isOpeningBracketToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isOpeningBracketToken(token), expected[index]);
                });
            });
        });

        describe("isNotOpeningBracketToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isNotOpeningBracketToken(token), !expected[index]);
                });
            });
        });
    }

    {
        const code = "if (obj && foo) { obj[foo](); }";
        const tokens = espree.parse(code, { ecmaVersion: 6, tokens: true }).tokens;
        const expected = [false, true, false, false, false, false, false, false, false, false, false, true, false, false, false];

        describe("isOpeningParenToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isOpeningParenToken(token), expected[index]);
                });
            });
        });

        describe("isNotOpeningParenToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isNotOpeningParenToken(token), !expected[index]);
                });
            });
        });
    }

    {
        const code = "if (obj && foo) { obj[foo](); }";
        const tokens = espree.parse(code, { ecmaVersion: 6, tokens: true }).tokens;
        const expected = [false, false, false, false, false, false, false, false, false, false, false, false, false, true, false];

        describe("isSemicolonToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isSemicolonToken(token), expected[index]);
                });
            });
        });

        describe("isNotSemicolonToken", () => {
            tokens.forEach((token, index) => {
                it(`should return ${expected[index]} for '${token.value}'.`, () => {
                    assert.strictEqual(astUtils.isNotSemicolonToken(token), !expected[index]);
                });
            });
        });
    }

    describe("isNullLiteral", () => {
        const EXPECTED_RESULTS = {
            null: true,
            "/abc/u": false,
            5: false,
            true: false,
            "'null'": false,
            foo: false
        };

        Object.keys(EXPECTED_RESULTS).forEach(key => {
            it(`returns ${EXPECTED_RESULTS[key]} for ${key}`, () => {
                const ast = espree.parse(key, { ecmaVersion: 6 });

                assert.strictEqual(astUtils.isNullLiteral(ast.body[0].expression), EXPECTED_RESULTS[key]);
            });
        });
    });

    describe("createGlobalLinebreakMatcher", () => {
        it("returns a regular expression with the g flag", () => {
            assert.instanceOf(astUtils.createGlobalLinebreakMatcher(), RegExp);
            assert(astUtils.createGlobalLinebreakMatcher().toString().endsWith("/gu"));
        });
        it("returns unique objects on each call", () => {
            const firstObject = astUtils.createGlobalLinebreakMatcher();
            const secondObject = astUtils.createGlobalLinebreakMatcher();

            assert.notStrictEqual(firstObject, secondObject);
        });
        describe("correctly matches linebreaks", () => {
            const LINE_COUNTS = {
                foo: 1,
                "foo\rbar": 2,
                "foo\n": 2,
                "foo\nbar": 2,
                "foo\r\nbar": 2,
                "foo\r\u2028bar": 3,
                "foo\u2029bar": 2
            };

            Object.keys(LINE_COUNTS).forEach(text => {
                it(text, () => {
                    assert.strictEqual(text.split(astUtils.createGlobalLinebreakMatcher()).length, LINE_COUNTS[text]);
                });
            });
        });
    });

    describe("canTokensBeAdjacent", () => {
        const CASES = new Map([
            [["foo", "bar"], false],
            [[";foo", "bar"], false],
            [[";", "bar"], true],
            [[")", "bar"], true],
            [["foo0", "bar"], false],
            [["foo;", "bar"], true],
            [["foo", "0"], false],
            [["of", ".2"], true],
            [["2", ".2"], false],
            [["of", "'foo'"], true],
            [["foo", "`bar`"], true],
            [["`foo`", "in"], true],
            [["of", "0.2"], false],
            [["of", "0."], false],
            [[".2", "foo"], false],
            [["2.", "foo"], false],
            [["+", "-"], true],
            [["++", "-"], true],
            [["+", "--"], true],
            [["++", "--"], true],
            [["-", "+"], true],
            [["--", "+"], true],
            [["-", "++"], true],
            [["--", "++"], true],
            [["+", "+"], false],
            [["-", "-"], false],
            [["++", "+"], false],
            [["--", "-"], false],
            [["+", "++"], false],
            [["-", "--"], false],
            [["a/", "b"], true],
            [["a/", "+b"], true],
            [["a+", "/^regex$/"], true],
            [["a/", "/^regex$/"], false],
            [["a+", "/**/"], true],
            [["a+", "/**/b"], true],
            [["//", "a"], false],
            [["a/", "/**/b"], false],
            [["a+", "//"], true],
            [["a+", "//\nb"], true],
            [["a/", "//\nb"], false],
            [["/**/", "b"], true],
            [["a/**/", "b"], true],
            [["/**/a", "b"], false],
            [["a", "/**/b"], true],
            [["a", "b/**/"], false],
            [["a", "//\nb"], true],
            [["a", "b//"], false],
            [["#!/usr/bin/env node", "("], false],
            [["123invalidtoken", "("], false],
            [["(", "123invalidtoken"], false],
            [["(", "1n"], true],
            [["1n", "+"], true],
            [["1n", "in"], false],
            [["return", "#x"], true],
            [["yield", "#x"], true],
            [["get", "#x"], true]
        ]);

        CASES.forEach((expectedResult, tokenStrings) => {
            it(tokenStrings.join(", "), () => {
                assert.strictEqual(astUtils.canTokensBeAdjacent(tokenStrings[0], tokenStrings[1]), expectedResult);
            });
        });

        it("#!/usr/bin/env node, (", () => {
            assert.strictEqual(
                astUtils.canTokensBeAdjacent(
                    { type: "Shebang", value: "#!/usr/bin/env node" },
                    { type: "Punctuator", value: "(" }
                ),
                false
            );
        });
    });

    describe("equalTokens", () => {
        it("should return true if tokens are equal", () => {
            const code = "a=0;a=0;";
            const ast = espree.parse(code, ESPREE_CONFIG);
            const sourceCode = new SourceCode(code, ast);

            assert.strictEqual(astUtils.equalTokens(ast.body[0], ast.body[1], sourceCode), true);
        });

        it("should return false if tokens are not equal", () => {
            const code = "a=0;a=1;";
            const ast = espree.parse(code, ESPREE_CONFIG);
            const sourceCode = new SourceCode(code, ast);

            assert.strictEqual(astUtils.equalTokens(ast.body[0], ast.body[1], sourceCode), false);
        });
    });

    describe("equalLiteralValue", () => {
        describe("should return true if two regex values are same, even if it's not supported natively.", () => {
            const patterns = [
                {
                    nodeA: {
                        type: "Literal",
                        value: /(?:)/u,
                        regex: { pattern: "(?:)", flags: "u" }
                    },
                    nodeB: {
                        type: "Literal",
                        value: /(?:)/u,
                        regex: { pattern: "(?:)", flags: "u" }
                    },
                    expected: true
                },
                {
                    nodeA: {
                        type: "Literal",
                        value: null,
                        regex: { pattern: "(?:)", flags: "u" }
                    },
                    nodeB: {
                        type: "Literal",
                        value: null,
                        regex: { pattern: "(?:)", flags: "u" }
                    },
                    expected: true
                },
                {
                    nodeA: {
                        type: "Literal",
                        value: null,
                        regex: { pattern: "(?:)", flags: "u" }
                    },
                    nodeB: {
                        type: "Literal",
                        value: /(?:)/, // eslint-disable-line require-unicode-regexp -- Checking non-Unicode regex
                        regex: { pattern: "(?:)", flags: "" }
                    },
                    expected: false
                },
                {
                    nodeA: {
                        type: "Literal",
                        value: null,
                        regex: { pattern: "(?:a)", flags: "u" }
                    },
                    nodeB: {
                        type: "Literal",
                        value: null,
                        regex: { pattern: "(?:b)", flags: "u" }
                    },
                    expected: false
                }
            ];

            for (const { nodeA, nodeB, expected } of patterns) {
                it(`should return ${expected} if it compared ${util.format("%o", nodeA)} and ${util.format("%o", nodeB)}`, () => {
                    assert.strictEqual(astUtils.equalLiteralValue(nodeA, nodeB), expected);
                });
            }
        });

        describe("should return true if two bigint values are same, even if it's not supported natively.", () => {
            const patterns = [
                {
                    nodeA: {
                        type: "Literal",
                        value: null,
                        bigint: "1"
                    },
                    nodeB: {
                        type: "Literal",
                        value: null,
                        bigint: "1"
                    },
                    expected: true
                },
                {
                    nodeA: {
                        type: "Literal",
                        value: null,
                        bigint: "1"
                    },
                    nodeB: {
                        type: "Literal",
                        value: null,
                        bigint: "2"
                    },
                    expected: false
                },
                {
                    nodeA: {
                        type: "Literal",
                        value: 1n,
                        bigint: "1"
                    },
                    nodeB: {
                        type: "Literal",
                        value: 1n,
                        bigint: "1"
                    },
                    expected: true
                },
                {
                    nodeA: {
                        type: "Literal",
                        value: 1n,
                        bigint: "1"
                    },
                    nodeB: {
                        type: "Literal",
                        value: 2n,
                        bigint: "2"
                    },
                    expected: false
                }
            ];

            for (const { nodeA, nodeB, expected } of patterns) {
                it(`should return ${expected} if it compared ${util.format("%o", nodeA)} and ${util.format("%o", nodeB)}`, () => {
                    assert.strictEqual(astUtils.equalLiteralValue(nodeA, nodeB), expected);
                });
            }
        });
    });

    describe("hasOctalOrNonOctalDecimalEscapeSequence", () => {

        /* eslint-disable quote-props -- Make consistent here for readability */
        const expectedResults = {
            "\\1": true,
            "\\2": true,
            "\\7": true,
            "\\00": true,
            "\\01": true,
            "\\02": true,
            "\\07": true,
            "\\08": true,
            "\\09": true,
            "\\10": true,
            "\\12": true,
            " \\1": true,
            "\\1 ": true,
            "a\\1": true,
            "\\1a": true,
            "a\\1a": true,
            " \\01": true,
            "\\01 ": true,
            "a\\01": true,
            "\\01a": true,
            "a\\01a": true,
            "a\\08a": true,
            "\\0\\1": true,
            "\\0\\01": true,
            "\\0\\08": true,
            "\\n\\1": true,
            "\\n\\01": true,
            "\\n\\08": true,
            "\\\\\\1": true,
            "\\\\\\01": true,
            "\\\\\\08": true,
            "\\8": true,
            "\\9": true,
            "a\\8a": true,
            "\\0\\8": true,
            "\\8\\0": true,
            "\\80": true,
            "\\81": true,
            "\\\\\\8": true,
            "\\\n\\1": true,
            "foo\\\nbar\\2baz": true,
            "\\\n\\8": true,
            "foo\\\nbar\\9baz": true,

            "\\0": false,
            " \\0": false,
            "\\0 ": false,
            "a\\0": false,
            "\\0a": false,
            "\\\\": false,
            "\\\\0": false,
            "\\\\01": false,
            "\\\\08": false,
            "\\\\1": false,
            "\\\\12": false,
            "\\\\\\0": false,
            "\\0\\\\": false,
            "0": false,
            "1": false,
            "8": false,
            "01": false,
            "08": false,
            "80": false,
            "12": false,
            "\\a": false,
            "\\n": false,
            "\\\n": false,
            "foo\\\nbar": false,
            "128\\\n349": false
        };
        /* eslint-enable quote-props -- Make consistent here for readability */

        Object.keys(expectedResults).forEach(key => {
            it(`should return ${expectedResults[key]} for ${key}`, () => {
                const ast = espree.parse(`"${key}"`);

                assert.strictEqual(astUtils.hasOctalOrNonOctalDecimalEscapeSequence(ast.body[0].expression.raw), expectedResults[key]);
            });
        });
    });

    describe("isLogicalAssignmentOperator", () => {
        const expectedResults = {
            "&&=": true,
            "||=": true,
            "??=": true,
            "&&": false,
            "||": false,
            "??": false,
            "=": false,
            "&=": false,
            "|=": false,
            "+=": false,
            "**=": false,
            "==": false,
            "===": false
        };

        Object.entries(expectedResults).forEach(([key, value]) => {
            it(`should return ${value} for ${key}`, () => {
                assert.strictEqual(astUtils.isLogicalAssignmentOperator(key), value);
            });
        });
    });

    describe("isTopLevelExpressionStatement", () => {
        it("should return false for a Program node", () => {
            const node = { type: "Program", parent: null };

            assert.strictEqual(astUtils.isTopLevelExpressionStatement(node), false);
        });

        it("should return false if the node is not an ExpressionStatement", () => {
            linter.defineRule("checker", {
                create: mustCall(() => ({
                    ":expression": mustCall(node => {
                        assert.strictEqual(astUtils.isTopLevelExpressionStatement(node), false);
                    })
                }))
            });

            linter.verify("var foo = () => \"use strict\";", { rules: { checker: "error" }, parserOptions: { ecmaVersion: 2022 } });
        });

        const expectedResults = [
            ["if (foo) { \"use strict\"; }", "\"use strict\";", false],
            ["{ \"use strict\"; }", "\"use strict\";", false],
            ["switch (foo) { case bar: \"use strict\"; }", "\"use strict\";", false],
            ["foo; bar;", "foo;", true],
            ["foo; bar;", "bar;", true],
            ["function foo() { bar; }", "bar;", true],
            ["var foo = function () { foo(); };", "foo();", true],
            ["var foo = () => { 'bar'; }", "'bar';", true],
            ["\"use strict\"", "\"use strict\"", true],
            ["(`use strict`)", "(`use strict`)", true]
        ];

        expectedResults.forEach(([code, nodeText, expectedRetVal]) => {
            it(`should return ${expectedRetVal} for \`${nodeText}\` in \`${code}\``, () => {
                linter.defineRule("checker", {
                    create: mustCall(context => {
                        const assertForNode = mustCall(
                            node => assert.strictEqual(astUtils.isTopLevelExpressionStatement(node), expectedRetVal)
                        );

                        return ({
                            ExpressionStatement(node) {
                                if (context.sourceCode.getText(node) === nodeText) {
                                    assertForNode(node);
                                }
                            }
                        });
                    })
                });

                linter.verify(code, { rules: { checker: "error" }, parserOptions: { ecmaVersion: 2022 } });
            });
        });
    });

    describe("isStaticTemplateLiteral", () => {
        const expectedResults = {
            "``": true,
            "`foo`": true,
            "`foo${bar}`": false,
            "\"foo\"": false,
            "foo`bar`": false
        };

        Object.entries(expectedResults).forEach(([code, expectedResult]) => {
            it(`returns ${expectedResult} for ${code}`, () => {
                const ast = espree.parse(code, { ecmaVersion: 6 });

                assert.strictEqual(astUtils.isStaticTemplateLiteral(ast.body[0].expression), expectedResult);
            });
        });
    });

    describe("isDirective", () => {
        const expectedResults = [
            { code: '"use strict";', expectedRetVal: true },
            { code: '"use strict"; "use asm";', nodeText: '"use asm";', expectedRetVal: true },
            { code: 'const a = () => { "foo"; }', nodeText: '"foo";', expectedRetVal: true },
            { code: '"";', expectedRetVal: true },
            { code: '{ "foo"; }', nodeText: '"foo";', expectedRetVal: false },
            { code: "foo();", expectedRetVal: false },
            { code: '"foo" + "bar";', expectedRetVal: false },
            { code: "12345;", expectedRetVal: false },
            { code: "`foo`;", expectedRetVal: false },
            { code: "('foo');", expectedRetVal: false },
            { code: 'foo(); "use strict";', nodeText: '"use strict";', expectedRetVal: false }
        ];

        expectedResults.forEach(({ code, nodeText = code, expectedRetVal }) => {
            it(`should return ${expectedRetVal} for \`${nodeText}\` in \`${code}\``, () => {
                linter.defineRule("checker", {
                    create: mustCall(({ sourceCode }) => {
                        const assertForNode = mustCall(
                            node => assert.strictEqual(astUtils.isDirective(node), expectedRetVal)
                        );

                        return ({
                            ExpressionStatement(node) {
                                if (sourceCode.getText(node) === nodeText) {
                                    assertForNode(node);

                                    if (!expectedRetVal) {

                                        // The flow parser sets `directive` to null on non-directive ExpressionStatement nodes.
                                        node.directive = null;
                                        assertForNode(node);
                                    }
                                }
                            }
                        });
                    })
                });

                linter.verify(code, { rules: { checker: "error" }, parserOptions: { ecmaVersion: 2022 } });
            });
        });
    });
});