fix(getCheckMessage): add API to return check message (#2066)

* feat(getCheckMessage): add API to return check message

* throw when invalid

lib/core/utils/get-check-message.js

@@ -0,0 +1,21 @@
+/* global axe*/
+
+/**
+ * Get the pass, fail, or incomplete message for a check.
+ * @param {String} checkId The check id
+ * @param {String} type The message type ('pass', 'fail', or 'incomplete')
+ * @param {Object} [data] The check data
+ * @return {String}
+ */
+axe.utils.getCheckMessage = function getCheckMessage(checkId, type, data) {
+	const check = axe._audit.data.checks[checkId];
+
+	if (!check) {
+		throw new Error(`Cannot get message for unknown check: ${checkId}.`);
+	}
+	if (!check.messages[type]) {
+		throw new Error(`Check "${checkId}"" does not have a "${type}" message.`);
+	}
+
+	return axe.utils.processMessage(check.messages[type], data);
+};

test/core/utils/get-check-message.js

@@ -0,0 +1,59 @@
+describe('axe.utils.getCheckMessage', function() {
+	var getCheckMessage = axe.utils.getCheckMessage;
+
+	beforeEach(function() {
+		axe._audit = {
+			data: {
+				checks: {
+					'my-check': {
+						messages: {
+							pass: 'Pass message',
+							fail: 'Fail message',
+							incomplete: 'Incomplete message'
+						}
+					}
+				}
+			}
+		};
+	});
+
+	afterEach(function() {
+		axe._audit = undefined;
+	});
+
+	it('should return the pass message', function() {
+		assert.equal(getCheckMessage('my-check', 'pass'), 'Pass message');
+	});
+
+	it('should return the fail message', function() {
+		assert.equal(getCheckMessage('my-check', 'fail'), 'Fail message');
+	});
+
+	it('should return the incomplete message', function() {
+		assert.equal(
+			getCheckMessage('my-check', 'incomplete'),
+			'Incomplete message'
+		);
+	});
+
+	it('should handle data', function() {
+		axe._audit.data.checks['my-check'].messages.pass =
+			'Pass message with ${data.message}';
+		assert.equal(
+			getCheckMessage('my-check', 'pass', { message: 'hello world!' }),
+			'Pass message with hello world!'
+		);
+	});
+
+	it('should error when check does not exist', function() {
+		assert.throws(function() {
+			getCheckMessage('invalid-check', 'pass');
+		});
+	});
+
+	it('should error when check message does not exist', function() {
+		assert.throws(function() {
+			getCheckMessage('invalid-check', 'invalid');
+		});
+	});
+});