feat(expect): add ArrayOf asymmetric matcher

Author: icholy

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### Features
 
+- `[expect]` Add `ArrayOf` asymmetric matcher for validating array elements. **TODO: ADD LINK!**
 - `[babel-jest]` Add option `excludeJestPreset` to allow opting out of `babel-preset-jest` ([#15164](https://github.com/jestjs/jest/pull/15164))
 - `[jest-circus, jest-cli, jest-config]` Add `waitNextEventLoopTurnForUnhandledRejectionEvents` flag to minimise performance impact of correct detection of unhandled promise rejections introduced in [#14315](https://github.com/jestjs/jest/pull/14315) ([#14681](https://github.com/jestjs/jest/pull/14681))
 - `[jest-circus]` Add a `waitBeforeRetry` option to `jest.retryTimes` ([#14738](https://github.com/jestjs/jest/pull/14738))

docs/ExpectAPI.md

@@ -958,6 +958,44 @@ describe('not.arrayContaining', () => {
 });
 ```
 
+### `expect.arrayOf(value)`
+
+`expect.arrayOf(value)` matches a received array whose elements match the provided value. This is useful for asserting that every item in an array satisfies a particular condition or type.
+
+**Example:**
+
+```js
+test('all elements in array are strings', () => {
+  expect(['apple', 'banana', 'cherry']).toEqual(expect.arrayOf(expect.any(String)));
+});
+```
+
+This matcher is particularly useful for validating arrays containing complex structures:
+
+```js
+test('array of objects with specific properties', () => {
+  expect([
+    { id: 1, name: 'Alice' },
+    { id: 2, name: 'Bob' }
+  ]).toEqual(expect.arrayOf(expect.objectContaining({
+    id: expect.any(Number),
+    name: expect.any(String)
+  })));
+});
+```
+
+### `expect.not.arrayOf(matcher)`
+
+`expect.not.arrayOf(matcher)` matches a received array where not all elements match the provided matcher.
+
+**Example:**
+
+```js
+test('not all elements in array are strings', () => {
+  expect(['apple', 123, 'cherry']).toEqual(expect.not.arrayOf(expect.any(String)));
+});
+```
+
 ### `expect.closeTo(number, numDigits?)`
 
 `expect.closeTo(number, numDigits?)` is useful when comparing floating point numbers in object properties or array item. If you need to compare a number, please use `.toBeCloseTo` instead.

packages/expect/src/__tests__/asymmetricMatchers.test.ts

@@ -13,7 +13,9 @@ import {
   anything,
   arrayContaining,
   arrayNotContaining,
+  arrayOf,
   closeTo,
+  notArrayOf,
   notCloseTo,
   objectContaining,
   objectNotContaining,
@@ -514,3 +516,62 @@ describe('closeTo', () => {
     jestExpect(notCloseTo(1).asymmetricMatch('a')).toBe(false);
   });
 });
+
+test('ArrayOf matches', () => {
+  for (const test of [
+    arrayOf(1).asymmetricMatch([1]),
+    arrayOf(1).asymmetricMatch([1, 1, 1]),
+    arrayOf({a: 1}).asymmetricMatch([{a: 1}, {a: 1}]),
+    arrayOf(undefined).asymmetricMatch([undefined]),
+    arrayOf(null).asymmetricMatch([null]),
+    arrayOf([]).asymmetricMatch([[], []]),
+    arrayOf(any(String)).asymmetricMatch(['a', 'b', 'c']),
+  ]) {
+    jestExpect(test).toEqual(true);
+  }
+});
+
+test('ArrayOf does not match', () => {
+  for (const test of [
+    arrayOf(1).asymmetricMatch([2]),
+    arrayOf(1).asymmetricMatch([1, 2]),
+    arrayOf({a: 1}).asymmetricMatch([{a: 2}]),
+    arrayOf(undefined).asymmetricMatch([null]),
+    arrayOf(null).asymmetricMatch([undefined]),
+    arrayOf([]).asymmetricMatch([{}]),
+    arrayOf(1).asymmetricMatch(1),
+    arrayOf(1).asymmetricMatch('not an array'),
+    arrayOf(1).asymmetricMatch({}),
+    arrayOf(any(String)).asymmetricMatch([1, 2]),
+  ]) {
+    jestExpect(test).toEqual(false);
+  }
+});
+
+test('NotArrayOf matches', () => {
+  for (const test of [
+    notArrayOf(1).asymmetricMatch([2]),
+    notArrayOf(1).asymmetricMatch([1, 2]),
+    notArrayOf({a: 1}).asymmetricMatch([{a: 2}]),
+    notArrayOf(1).asymmetricMatch(1),
+    notArrayOf(1).asymmetricMatch('not an array'),
+    notArrayOf(1).asymmetricMatch({}),
+    notArrayOf(any(Number)).asymmetricMatch(['a', 'b']),
+  ]) {
+    jestExpect(test).toEqual(true);
+  }
+});
+
+test('NotArrayOf does not match', () => {
+  for (const test of [
+    notArrayOf(1).asymmetricMatch([1]),
+    notArrayOf(1).asymmetricMatch([1, 1, 1]),
+    notArrayOf({a: 1}).asymmetricMatch([{a: 1}, {a: 1}]),
+    notArrayOf(undefined).asymmetricMatch([undefined]),
+    notArrayOf(null).asymmetricMatch([null]),
+    notArrayOf([]).asymmetricMatch([[], []]),
+    notArrayOf(any(String)).asymmetricMatch(['a', 'b', 'c']),
+  ]) {
+    jestExpect(test).toEqual(false);
+  }
+});

packages/expect/src/asymmetricMatchers.ts

@@ -225,6 +225,27 @@ class ArrayContaining extends AsymmetricMatcher<Array<unknown>> {
   }
 }
 
+class ArrayOf extends AsymmetricMatcher<unknown> {
+  asymmetricMatch(other: unknown) {
+    const matcherContext = this.getMatcherContext();
+    const result =
+      Array.isArray(other) &&
+      other.every(item =>
+        equals(this.sample, item, matcherContext.customTesters),
+      );
+
+    return this.inverse ? !result : result;
+  }
+
+  toString() {
+    return `${this.inverse ? 'Not' : ''}ArrayOf`;
+  }
+
+  override getExpectedType() {
+    return 'array';
+  }
+}
+
 class ObjectContaining extends AsymmetricMatcher<
   Record<string | symbol, unknown>
 > {
@@ -383,6 +404,9 @@ export const arrayContaining = (sample: Array<unknown>): ArrayContaining =>
   new ArrayContaining(sample);
 export const arrayNotContaining = (sample: Array<unknown>): ArrayContaining =>
   new ArrayContaining(sample, true);
+export const arrayOf = (sample: unknown): ArrayOf => new ArrayOf(sample);
+export const notArrayOf = (sample: unknown): ArrayOf =>
+  new ArrayOf(sample, true);
 export const objectContaining = (
   sample: Record<string, unknown>,
 ): ObjectContaining => new ObjectContaining(sample);

packages/expect/src/index.ts

@@ -16,7 +16,9 @@ import {
   anything,
   arrayContaining,
   arrayNotContaining,
+  arrayOf,
   closeTo,
+  notArrayOf,
   notCloseTo,
   objectContaining,
   objectNotContaining,
@@ -397,13 +399,15 @@ expect.any = any;
 
 expect.not = {
   arrayContaining: arrayNotContaining,
+  arrayOf: notArrayOf,
   closeTo: notCloseTo,
   objectContaining: objectNotContaining,
   stringContaining: stringNotContaining,
   stringMatching: stringNotMatching,
 };
 
 expect.arrayContaining = arrayContaining;
+expect.arrayOf = arrayOf;
 expect.closeTo = closeTo;
 expect.objectContaining = objectContaining;
 expect.stringContaining = stringContaining;

packages/expect/src/types.ts

@@ -117,6 +117,7 @@ export interface AsymmetricMatchers {
   any(sample: unknown): AsymmetricMatcher;
   anything(): AsymmetricMatcher;
   arrayContaining(sample: Array<unknown>): AsymmetricMatcher;
+  arrayOf(sample: unknown): AsymmetricMatcher;
   closeTo(sample: number, precision?: number): AsymmetricMatcher;
   objectContaining(sample: Record<string, unknown>): AsymmetricMatcher;
   stringContaining(sample: string): AsymmetricMatcher;

packages/pretty-format/src/__tests__/AsymmetricMatcher.test.ts

@@ -78,6 +78,16 @@ test('arrayNotContaining()', () => {
 ]`);
 });
 
+test('arrayOf()', () => {
+  const result = prettyFormat(expect.arrayOf(expect.any(String)), options);
+  expect(result).toBe('ArrayOf Any<String>');
+});
+
+test('notArrayOf()', () => {
+  const result = prettyFormat(expect.not.arrayOf(expect.any(String)), options);
+  expect(result).toBe('NotArrayOf Any<String>');
+});
+
 test('objectContaining()', () => {
   const result = prettyFormat(expect.objectContaining({a: 'test'}), options);
   expect(result).toBe(`ObjectContaining {
@@ -183,6 +193,11 @@ test('supports multiple nested asymmetric matchers', () => {
           d: expect.stringContaining('jest'),
           e: expect.stringMatching('jest'),
           f: expect.objectContaining({test: 'case'}),
+          g: expect.arrayOf(
+            expect.objectContaining({
+              nested: expect.any(Number),
+            }),
+          ),
         }),
       },
     },
@@ -201,6 +216,9 @@ test('supports multiple nested asymmetric matchers', () => {
       "f": ObjectContaining {
         "test": "case",
       },
+      "g": ArrayOf ObjectContaining {
+        "nested": Any<Number>,
+      },
     },
   },
 }`);

packages/pretty-format/src/plugins/AsymmetricMatcher.ts

@@ -80,6 +80,19 @@ export const serialize: NewPlugin['serialize'] = (
     );
   }
 
+  if (stringedValue === 'ArrayOf' || stringedValue === 'NotArrayOf') {
+    if (++depth > config.maxDepth) {
+      return `[${stringedValue}]`;
+    }
+    return `${stringedValue + SPACE}${printer(
+      val.sample,
+      config,
+      indentation,
+      depth,
+      refs,
+    )}`;
+  }
+
   if (typeof val.toAsymmetricMatcher !== 'function') {
     throw new TypeError(
       `Asymmetric matcher ${val.constructor.name} does not implement toAsymmetricMatcher()`,