Repository: eslint/eslint
File: lib/rule-tester/rule-tester.js (JavaScript)

Code before:
	if (hasOwnProperty(item, "options")) {
		assert.ok(
			Array.isArray(item.options),
			"Optional test case property 'options' must be an array",
		);
	}
}

/**
 * Asserts that a valid test case object is valid.
 * A valid test case must specify a string value for 'code'.
 * Optional properties are checked for correct types.
 * @param {Object} item The valid test case object to check.
 * @param {Set<string>} seenTestCases Set of serialized test cases to check for duplicates.
 * @returns {void}
 * @throws {AssertionError} If the test case is not valid.
 */
function assertValidTestCase(item, seenTestCases) {
	// must not have x properties
	assert.ok(
		item.errors === void 0,
		"Valid test case must not have 'errors' property`",
	);
	assert.ok(
		item.output === void 0,
		"Valid test case must not have 'output' property`",
	);

	assertTestCommonProperties(item);
	checkDuplicateTestCase(item, seenTestCases);
}

/**
 * Asserts that the invalid test case object is valid.
 * An invalid test case must specify a string value for 'code' and must have 'errors' property.
 * Optional properties are checked for correct types.
 * @param {Object} item The invalid test case object to check.
 * @param {Set<string>} seenTestCases Set of serialized test cases to check for duplicates.
 * @param {string} ruleName The name of the rule being tested.
 * @returns {void}
 * @throws {AssertionError} If the test case is not valid.
 */
function assertInvalidTestCase(item, seenTestCases, ruleName) {
	assertTestCommonProperties(item);

	assertErrorsProperty(item.errors, ruleName);

	// 'output' is optional, but if it exists it must be a string or null
	if (hasOwnProperty(item, "output")) {
		assert.ok(
			item.output === null || typeof item.output === "string",

Review comment (suggestion):
```suggestion
		"Valid test case must not have 'output' property",
```

Code after:
	if (hasOwnProperty(item, "options")) {
		assert.ok(
			Array.isArray(item.options),
			"Optional test case property 'options' must be an array",
		);
	}
}

/**
 * Asserts that a valid test case object is valid.
 * A valid test case must specify a string value for 'code'.
 * Optional properties are checked for correct types.
 * @param {Object} item The valid test case object to check.
 * @param {Set<string>} seenTestCases Set of serialized test cases to check for duplicates.
 * @returns {void}
 * @throws {AssertionError} If the test case is not valid.
 */
function assertValidTestCase(item, seenTestCases) {
	// must not have properties of invalid test cases
	assert.ok(
		item.errors === void 0,
		"Valid test case must not have 'errors' property",
	);
	assert.ok(
		item.output === void 0,
		"Valid test case must not have 'output' property",
	);

	assertTestCommonProperties(item);
	checkDuplicateTestCase(item, seenTestCases);
}

/**
 * Asserts that the invalid test case object is valid.
 * An invalid test case must specify a string value for 'code' and must have 'errors' property.
 * Optional properties are checked for correct types.
 * @param {Object} item The invalid test case object to check.
 * @param {Set<string>} seenTestCases Set of serialized test cases to check for duplicates.
 * @param {string} ruleName The name of the rule being tested.
 * @returns {void}
 * @throws {AssertionError} If the test case is not valid.
 */
function assertInvalidTestCase(item, seenTestCases, ruleName) {
	assertTestCommonProperties(item);

	assertErrorsProperty(item.errors, ruleName);

	// 'output' is optional, but if it exists it must be a string or null
	if (hasOwnProperty(item, "output")) {
		assert.ok(
			item.output === null || typeof item.output === "string",