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feat: create prefer-equality-matcher rule
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G-Rath committed Jan 15, 2022
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1 change: 1 addition & 0 deletions README.md
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Expand Up @@ -178,6 +178,7 @@ installations requiring long-term consistency.
| [no-test-return-statement](docs/rules/no-test-return-statement.md) | Disallow explicitly returning from tests | | |
| [prefer-called-with](docs/rules/prefer-called-with.md) | Suggest using `toBeCalledWith()` or `toHaveBeenCalledWith()` | | |
| [prefer-comparison-matcher](docs/rules/prefer-comparison-matcher.md) | Suggest using the built-in comparison matchers | | ![fixable][] |
| [prefer-equality-matcher](docs/rules/prefer-equality-matcher.md) | Suggest using the built-in equality matchers | | ![suggest][] |
| [prefer-expect-assertions](docs/rules/prefer-expect-assertions.md) | Suggest using `expect.assertions()` OR `expect.hasAssertions()` | | ![suggest][] |
| [prefer-expect-resolves](docs/rules/prefer-expect-resolves.md) | Prefer `await expect(...).resolves` over `expect(await ...)` syntax | | ![fixable][] |
| [prefer-hooks-on-top](docs/rules/prefer-hooks-on-top.md) | Suggest having hooks before any test cases | | |
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29 changes: 29 additions & 0 deletions docs/rules/prefer-equality-matcher.md
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# Suggest using the built-in equality matchers (`prefer-equality-matcher`)

Jest has built-in matchers for expecting equality which allow for more readable
tests and error messages if an expectation fails.

## Rule details

This rule checks for _strict_ equality checks (`===` & `!==`) in tests that
could be replaced with one of the following built-in equality matchers:

- `toBe`
- `toEqual`
- `toStrictEqual`

Examples of **incorrect** code for this rule:

```js
expect(x === 5).toBe(true);
expect(name === 'Carl').not.toEqual(true);
expect(myObj !== thatObj).toStrictEqual(true);
```

Examples of **correct** code for this rule:

```js
expect(x).toBe(5);
expect(name).not.toEqual('Carl');
expect(myObj).toStrictEqual(thatObj);
```
1 change: 1 addition & 0 deletions src/__tests__/__snapshots__/rules.test.ts.snap
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Expand Up @@ -36,6 +36,7 @@ Object {
"jest/no-test-return-statement": "error",
"jest/prefer-called-with": "error",
"jest/prefer-comparison-matcher": "error",
"jest/prefer-equality-matcher": "error",
"jest/prefer-expect-assertions": "error",
"jest/prefer-expect-resolves": "error",
"jest/prefer-hooks-on-top": "error",
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2 changes: 1 addition & 1 deletion src/__tests__/rules.test.ts
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Expand Up @@ -2,7 +2,7 @@ import { existsSync } from 'fs';
import { resolve } from 'path';
import plugin from '../';

const numberOfRules = 44;
const numberOfRules = 45;
const ruleNames = Object.keys(plugin.rules);
const deprecatedRules = Object.entries(plugin.rules)
.filter(([, rule]) => rule.meta.deprecated)
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155 changes: 155 additions & 0 deletions src/rules/__tests__/prefer-equality-matcher.test.ts
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import { TSESLint } from '@typescript-eslint/experimental-utils';
import rule from '../prefer-equality-matcher';
import { espreeParser } from './test-utils';

const ruleTester = new TSESLint.RuleTester({
parser: espreeParser,
parserOptions: {
ecmaVersion: 2015,
},
});

type RuleMessages<TRuleModule extends TSESLint.RuleModule<string>> =
TRuleModule extends TSESLint.RuleModule<infer TMessageIds>
? TMessageIds
: never;

type RuleSuggestionOutput = TSESLint.SuggestionOutput<
RuleMessages<typeof rule>
>;

const expectSuggestions = (
output: (equalityMatcher: string) => string,
): RuleSuggestionOutput[] => {
return ['toBe', 'toEqual', 'toStrictEqual'].map<RuleSuggestionOutput>(
equalityMatcher => ({
messageId: 'suggestEqualityMatcher',
data: { equalityMatcher },
output: output(equalityMatcher),
}),
);
};

ruleTester.run('prefer-equality-matcher: ===', rule, {
valid: [
'expect(a == 1).toBe(true)',
'expect(1 == a).toBe(true)',
'expect(a == b).toBe(true)',
],
invalid: [
{
code: 'expect(a === b).toBe(true);',
errors: [
{
messageId: 'useEqualityMatcher',
suggestions: expectSuggestions(
equalityMatcher => `expect(a).${equalityMatcher}(b);`,
),
column: 17,
line: 1,
},
],
},
{
code: 'expect(a === b).toBe(false);',
errors: [
{
messageId: 'useEqualityMatcher',
suggestions: expectSuggestions(
equalityMatcher => `expect(a).not.${equalityMatcher}(b);`,
),
column: 17,
line: 1,
},
],
},
{
code: 'expect(a === b).not.toBe(true);',
errors: [
{
messageId: 'useEqualityMatcher',
suggestions: expectSuggestions(
equalityMatcher => `expect(a).not.${equalityMatcher}(b);`,
),
column: 17,
line: 1,
},
],
},
{
code: 'expect(a === b).not.toBe(false);',
errors: [
{
messageId: 'useEqualityMatcher',
suggestions: expectSuggestions(
equalityMatcher => `expect(a).${equalityMatcher}(b);`,
),
column: 17,
line: 1,
},
],
},
],
});

ruleTester.run('prefer-equality-matcher: !==', rule, {
valid: [
'expect(a != 1).toBe(true)',
'expect(1 != a).toBe(true)',
'expect(a != b).toBe(true)',
],
invalid: [
{
code: 'expect(a !== b).toBe(true);',
errors: [
{
messageId: 'useEqualityMatcher',
suggestions: expectSuggestions(
equalityMatcher => `expect(a).not.${equalityMatcher}(b);`,
),
column: 17,
line: 1,
},
],
},
{
code: 'expect(a !== b).toBe(false);',
errors: [
{
messageId: 'useEqualityMatcher',
suggestions: expectSuggestions(
equalityMatcher => `expect(a).${equalityMatcher}(b);`,
),
column: 17,
line: 1,
},
],
},
{
code: 'expect(a !== b).not.toBe(true);',
errors: [
{
messageId: 'useEqualityMatcher',
suggestions: expectSuggestions(
equalityMatcher => `expect(a).${equalityMatcher}(b);`,
),
column: 17,
line: 1,
},
],
},
{
code: 'expect(a !== b).not.toBe(false);',
errors: [
{
messageId: 'useEqualityMatcher',
suggestions: expectSuggestions(
equalityMatcher => `expect(a).not.${equalityMatcher}(b);`,
),
column: 17,
line: 1,
},
],
},
],
});
138 changes: 138 additions & 0 deletions src/rules/prefer-equality-matcher.ts
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import {
AST_NODE_TYPES,
TSESLint,
TSESTree,
} from '@typescript-eslint/experimental-utils';
import {
MaybeTypeCast,
ModifierName,
ParsedEqualityMatcherCall,
ParsedExpectMatcher,
createRule,
followTypeAssertionChain,
isExpectCall,
isParsedEqualityMatcherCall,
parseExpectCall,
} from './utils';

const isBooleanLiteral = (
node: TSESTree.Node,
): node is TSESTree.BooleanLiteral =>
node.type === AST_NODE_TYPES.Literal && typeof node.value === 'boolean';

type ParsedBooleanEqualityMatcherCall = ParsedEqualityMatcherCall<
MaybeTypeCast<TSESTree.BooleanLiteral>
>;

/**
* Checks if the given `ParsedExpectMatcher` is a call to one of the equality matchers,
* with a boolean literal as the sole argument.
*
* @example javascript
* toBe(true);
* toEqual(false);
*
* @param {ParsedExpectMatcher} matcher
*
* @return {matcher is ParsedBooleanEqualityMatcher}
*/
const isBooleanEqualityMatcher = (
matcher: ParsedExpectMatcher,
): matcher is ParsedBooleanEqualityMatcherCall =>
isParsedEqualityMatcherCall(matcher) &&
isBooleanLiteral(followTypeAssertionChain(matcher.arguments[0]));

export default createRule({
name: __filename,
meta: {
docs: {
category: 'Best Practices',
description: 'Suggest using the built-in equality matchers',
recommended: false,
suggestion: true,
},
messages: {
useEqualityMatcher: 'Prefer using one of the equality matchers instead',
suggestEqualityMatcher: 'Use `{{ equalityMatcher }}`',
},
hasSuggestions: true,
type: 'suggestion',
schema: [],
},
defaultOptions: [],
create(context) {
return {
CallExpression(node) {
if (!isExpectCall(node)) {
return;
}

const {
expect: {
arguments: [comparison],
range: [, expectCallEnd],
},
matcher,
modifier,
} = parseExpectCall(node);

if (
!matcher ||
comparison?.type !== AST_NODE_TYPES.BinaryExpression ||
(comparison.operator !== '===' && comparison.operator !== '!==') ||
!isBooleanEqualityMatcher(matcher)
) {
return;
}

const matcherValue = followTypeAssertionChain(
matcher.arguments[0],
).value;

// we need to negate the expectation if the current expected
// value is itself negated by the "not" modifier
const addNotModifier =
(comparison.operator === '!==' ? !matcherValue : matcherValue) ===
!!modifier;

const buildFixer =
(equalityMatcher: string): TSESLint.ReportFixFunction =>
fixer => {
const sourceCode = context.getSourceCode();

return [
// replace the comparison argument with the left-hand side of the comparison
fixer.replaceText(
comparison,
sourceCode.getText(comparison.left),
),
// replace the current matcher & modifier with the preferred matcher
fixer.replaceTextRange(
[expectCallEnd, matcher.node.range[1]],
addNotModifier
? `.${ModifierName.not}.${equalityMatcher}`
: `.${equalityMatcher}`,
),
// replace the matcher argument with the right-hand side of the comparison
fixer.replaceText(
matcher.arguments[0],
sourceCode.getText(comparison.right),
),
];
};

context.report({
messageId: 'useEqualityMatcher',
suggest: ['toBe', 'toEqual', 'toStrictEqual'].map(
equalityMatcher => ({
messageId: 'suggestEqualityMatcher',
data: { equalityMatcher },
fix: buildFixer(equalityMatcher),
}),
),
node: (modifier || matcher).node.property,
});
},
};
},
});

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