fix!: stricter rule tester assertions for valid test cases (#20125)

aladdin-add · mdjermanovic · web-flow · commit ca4d3b40085d · 2025-11-16T16:10:33.000+01:00
* fix!: valid test cases must not have errors/output properties. fixes #18960 * fix: remove useless errors/output * fix: remove unused errors * fix: review suggestions * fix: review suggestions * docs: add migrating guide * chore: review suggestions Co-authored-by: Milos Djermanovic <milos.djermanovic@gmail.com> --------- Co-authored-by: Milos Djermanovic <milos.djermanovic@gmail.com>
diff --git a/docs/src/use/migrate-to-10.0.0.md b/docs/src/use/migrate-to-10.0.0.md
@@ -35,6 +35,7 @@ The lists below are ordered roughly by the number of users each change is expect
 - [Fixer methods now require string `text` arguments](#fixer-text-must-be-string)
 - [New requirements for `ScopeManager` implementations](#scope-manager)
 - [Removal of deprecated `context` members](#rule-context)
+- [Prohibiting `errors` or `output` of valid RuleTester test cases](#stricter-rule-tester)
 
 ### Breaking changes for integration developers
 
@@ -285,6 +286,34 @@ The removed `context` properties must be done manually as there may not be a dir
 
 **Related issue(s):** [eslint/eslint#16999](https://github.com/eslint/eslint/issues/16999)
 
+## <a name="stricter-rule-tester"></a> Prohibiting `errors` or `output` of valid RuleTester test cases
+
+In ESLint v10.0.0, the RuleTester has become more strict about test case structure. Valid test cases (those that should not produce any linting errors) are no longer allowed to have `errors` or `output` properties.
+
+​What changed:​​
+
+- Previously, valid test cases could include `errors` or `output` properties, which were ignored.
+- Now, including these properties in valid test cases will cause the test to fail.
+
+Example of invalid usage:​
+
+```js
+// This will now throw an error in ESLint v10.0.0
+const validTestCases = [
+	{
+		code: "const foo = 'bar';",
+		errors: 0, // ❌ Not allowed in valid test cases
+		output: "const foo = 'bar';", // ❌ Not allowed in valid test cases
+	},
+];
+
+ruleTester.run("rule-id", rule, { valid: validTestCases, invalid: [] });
+```
+
+**To address:** Remove any `errors`/`output` properties from valid test cases.
+
+**Related issue(s):** [#18960](https://github.com/eslint/eslint/issues/18960)
+
 ## <a name="lintmessage-nodetype-removed"></a> Removal of `nodeType` property in `LintMessage` objects
 
 In ESLint v10.0.0, the deprecated `nodeType` property on `LintMessage` objects has been removed. This affects consumers of the Node.js API (for example, custom formatters and editor/tool integrations) that previously relied on `message.nodeType`.
diff --git a/lib/rule-tester/rule-tester.js b/lib/rule-tester/rule-tester.js
@@ -543,6 +543,16 @@ function assertTestCommonProperties(item) {
  * @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);
 }
diff --git a/tests/lib/rule-tester/rule-tester.js b/tests/lib/rule-tester/rule-tester.js
@@ -731,6 +731,57 @@ describe("RuleTester", () => {
 		});
 	});
 
+	describe("assert valid test cases", () => {
+		/**
+		 * Runs valid tests
+		 * @param {Array<string|object>} valid Valid tests
+		 * @returns {void}
+		 */
+		function runValidTests(valid) {
+			ruleTester.run(
+				"no-eval",
+				require("../../fixtures/testers/rule-tester/no-eval"),
+				{ valid, invalid: [] },
+			);
+		}
+
+		it("Valid test case must not have 'errors' property", () => {
+			assert.throws(() => {
+				runValidTests([{ code: "", errors: 1 }]);
+			}, /Valid test case must not have 'errors' property/u);
+
+			assert.throws(() => {
+				runValidTests([{ code: "", errors: [{ message: "foo" }] }]);
+			}, /Valid test case must not have 'errors' property/u);
+
+			assert.throws(() => {
+				runValidTests([{ code: "", errors: 0 }]);
+			}, /Valid test case must not have 'errors' property/u);
+
+			assert.throws(() => {
+				runValidTests([{ code: "", errors: [] }]);
+			}, /Valid test case must not have 'errors' property/u);
+		});
+
+		it("Valid test case can have 'errors' property set to undefined", () => {
+			runValidTests([{ code: "", errors: void 0 }]);
+		});
+
+		it("Valid test case must not have 'output' property", () => {
+			assert.throws(() => {
+				runValidTests([{ code: "", output: "" }]);
+			}, /Valid test case must not have 'output' property/u);
+
+			assert.throws(() => {
+				runValidTests([{ code: "", output: null }]);
+			}, /Valid test case must not have 'output' property/u);
+		});
+
+		it("Valid test case can have 'output' property set to undefined", () => {
+			runValidTests([{ code: "", output: void 0 }]);
+		});
+	});
+
 	it("should not throw an error when everything passes", () => {
 		ruleTester.run(
 			"no-eval",
diff --git a/tests/lib/rules/key-spacing.js b/tests/lib/rules/key-spacing.js
@@ -677,7 +677,6 @@ ruleTester.run("key-spacing", rule, {
 				},
 			],
 			languageOptions: { ecmaVersion: 6 },
-			errors: [],
 		},
 		{
 			code: [
diff --git a/tests/lib/rules/no-invalid-this.js b/tests/lib/rules/no-invalid-this.js
@@ -77,7 +77,7 @@ function extractPatterns(patterns, type) {
 			applyCondition(thisPattern);
 
 			if (type === "valid") {
-				thisPattern.errors = [];
+				thisPattern.errors = void 0;
 			} else {
 				thisPattern.code += " /* should error */";
 			}
diff --git a/tests/lib/rules/no-restricted-imports.js b/tests/lib/rules/no-restricted-imports.js
@@ -3736,11 +3736,6 @@ ruleTesterTypeScript.run("no-restricted-imports", rule, {
 					],
 				},
 			],
-			errors: [
-				{
-					messageId: "path",
-				},
-			],
 		},
 		{
 			code: `export { type bar, baz } from "foo";`,
diff --git a/tests/lib/rules/no-undef.js b/tests/lib/rules/no-undef.js
@@ -164,17 +164,14 @@ ruleTester.run("no-undef", rule, {
 		{
 			code: "let a; class C { static {} } a;",
 			languageOptions: { ecmaVersion: 2022 },
-			errors: [{ messageId: "undef", data: { name: "a" } }],
 		},
 		{
 			code: "var a; class C { static {} } a;",
 			languageOptions: { ecmaVersion: 2022 },
-			errors: [{ messageId: "undef", data: { name: "a" } }],
 		},
 		{
 			code: "a; class C { static {} } var a;",
 			languageOptions: { ecmaVersion: 2022 },
-			errors: [{ messageId: "undef", data: { name: "a" } }],
 		},
 		{
 			code: "class C { static { C; } }",
diff --git a/tests/lib/rules/prefer-const.js b/tests/lib/rules/prefer-const.js
@@ -227,33 +227,11 @@ ruleTester.run("prefer-const", rule, {
 		},
 		{
 			code: "class C { static { let a, b; if (foo) { ({ a, b } = foo); } } }",
-			output: null,
 			languageOptions: { ecmaVersion: 2022 },
-			errors: [
-				{
-					messageId: "useConst",
-					data: { name: "a" },
-				},
-				{
-					messageId: "useConst",
-					data: { name: "b" },
-				},
-			],
 		},
 		{
 			code: "class C { static { let a, b; if (foo) ({ a, b } = foo); } }",
-			output: null,
 			languageOptions: { ecmaVersion: 2022 },
-			errors: [
-				{
-					messageId: "useConst",
-					data: { name: "a" },
-				},
-				{
-					messageId: "useConst",
-					data: { name: "b" },
-				},
-			],
 		},
 		{
 			code: "class C { static { a; } } let a = 1; ",

Original file line number	Diff line number	Diff line change
`@@ -677,7 +677,6 @@ ruleTester.run("key-spacing", rule, {`
`677`	`677`	`},`
`678`	`678`	`],`
`679`	`679`	`languageOptions: { ecmaVersion: 6 },`
`680`		`- errors: [],`
`681`	`680`	`},`
`682`	`681`	`{`
`683`	`682`	`code: [`
Original file line number	Diff line number	Diff line change
`@@ -77,7 +77,7 @@ function extractPatterns(patterns, type) {`
`77`	`77`	`applyCondition(thisPattern);`
`78`	`78`
`79`	`79`	`if (type === "valid") {`
`80`		`- thisPattern.errors = [];`
	`80`	`+ thisPattern.errors = void 0;`
`81`	`81`	`} else {`
`82`	`82`	`thisPattern.code += " /* should error */";`
`83`	`83`	`}`
Original file line number	Diff line number	Diff line change
`@@ -164,17 +164,14 @@ ruleTester.run("no-undef", rule, {`
`164`	`164`	`{`
`165`	`165`	`code: "let a; class C { static {} } a;",`
`166`	`166`	`languageOptions: { ecmaVersion: 2022 },`
`167`		`- errors: [{ messageId: "undef", data: { name: "a" } }],`
`168`	`167`	`},`
`169`	`168`	`{`
`170`	`169`	`code: "var a; class C { static {} } a;",`
`171`	`170`	`languageOptions: { ecmaVersion: 2022 },`
`172`		`- errors: [{ messageId: "undef", data: { name: "a" } }],`
`173`	`171`	`},`
`174`	`172`	`{`
`175`	`173`	`code: "a; class C { static {} } var a;",`
`176`	`174`	`languageOptions: { ecmaVersion: 2022 },`
`177`		`- errors: [{ messageId: "undef", data: { name: "a" } }],`
`178`	`175`	`},`
`179`	`176`	`{`
`180`	`177`	`code: "class C { static { C; } }",`