Extract definitions for expect and mocks from generic test setup to standalone modules

jest/integration/runtime/expect.js

@@ -0,0 +1,235 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+import {ensureMockFunction} from './mocks';
+import deepEqual from 'deep-equal';
+import {diff} from 'jest-diff';
+
+class ErrorWithCustomBlame extends Error {
+  // Initially 5 to ignore all the frames from Babel helpers to instantiate this
+  // custom error class.
+  #ignoredFrameCount: number = 5;
+  #cachedProcessedStack: ?string;
+  #customStack: ?string;
+
+  blameToPreviousFrame(): this {
+    this.#cachedProcessedStack = null;
+    this.#ignoredFrameCount++;
+    return this;
+  }
+
+  // $FlowExpectedError[unsafe-getters-setters]
+  get stack(): string {
+    if (this.#cachedProcessedStack == null) {
+      const originalStack = this.#customStack ?? super.stack;
+
+      const lines = originalStack.split('\n');
+      const index = lines.findIndex(line =>
+        /at (.*) \((.*):(\d+):(\d+)\)/.test(line),
+      );
+      lines.splice(index > -1 ? index : 1, this.#ignoredFrameCount);
+      this.#cachedProcessedStack = lines.join('\n');
+    }
+
+    return this.#cachedProcessedStack;
+  }
+
+  // $FlowExpectedError[unsafe-getters-setters]
+  set stack(value: string) {
+    this.#cachedProcessedStack = null;
+    this.#customStack = value;
+  }
+
+  static fromError(error: Error): ErrorWithCustomBlame {
+    const errorWithCustomBlame = new ErrorWithCustomBlame(error.message);
+    // In this case we're inheriting the error and we don't know if the stack
+    // contains helpers that we need to ignore.
+    errorWithCustomBlame.#ignoredFrameCount = 0;
+    errorWithCustomBlame.stack = error.stack;
+    return errorWithCustomBlame;
+  }
+}
+
+class Expect {
+  #received: mixed;
+  #isNot: boolean = false;
+
+  constructor(received: mixed) {
+    this.#received = received;
+  }
+
+  // $FlowExpectedError[unsafe-getters-setters]
+  get not(): this {
+    this.#isNot = !this.#isNot;
+    return this;
+  }
+
+  toEqual(expected: mixed): void {
+    const pass = deepEqual(this.#received, expected, {strict: true});
+    if (!this.#isExpectedResult(pass)) {
+      throw new ErrorWithCustomBlame(
+        `Expected${this.#maybeNotLabel()} to equal:\n${
+          diff(expected, this.#received, {
+            contextLines: 1,
+            expand: false,
+            omitAnnotationLines: true,
+          }) ?? 'Failed to compare outputs'
+        }`,
+      ).blameToPreviousFrame();
+    }
+  }
+
+  toBe(expected: mixed): void {
+    const pass = this.#received === expected;
+    if (!this.#isExpectedResult(pass)) {
+      throw new ErrorWithCustomBlame(
+        `Expected${this.#maybeNotLabel()} ${String(expected)} but received ${String(this.#received)}.`,
+      ).blameToPreviousFrame();
+    }
+  }
+
+  toBeInstanceOf(expected: Class<mixed>): void {
+    const pass = this.#received instanceof expected;
+    if (!this.#isExpectedResult(pass)) {
+      throw new ErrorWithCustomBlame(
+        `expected ${String(this.#received)}${this.#maybeNotLabel()} to be an instance of ${String(expected)}`,
+      ).blameToPreviousFrame();
+    }
+  }
+
+  toBeCloseTo(expected: number, precision: number = 2): void {
+    const pass =
+      Math.abs(expected - Number(this.#received)) < Math.pow(10, -precision);
+    if (!this.#isExpectedResult(pass)) {
+      throw new ErrorWithCustomBlame(
+        `Expected ${String(this.#received)}${this.#maybeNotLabel()} to be close to ${expected}`,
+      ).blameToPreviousFrame();
+    }
+  }
+
+  toBeNull(): void {
+    const pass = this.#received == null;
+    if (!this.#isExpectedResult(pass)) {
+      throw new ErrorWithCustomBlame(
+        `Expected ${String(this.#received)}${this.#maybeNotLabel()} to be null`,
+      ).blameToPreviousFrame();
+    }
+  }
+
+  toThrow(expected?: string): void {
+    if (expected != null && typeof expected !== 'string') {
+      throw new ErrorWithCustomBlame(
+        'toThrow() implementation only accepts strings as arguments.',
+      ).blameToPreviousFrame();
+    }
+
+    let pass = false;
+    try {
+      // $FlowExpectedError[not-a-function]
+      this.#received();
+    } catch (error) {
+      pass = expected != null ? error.message === expected : true;
+    }
+    if (!this.#isExpectedResult(pass)) {
+      throw new ErrorWithCustomBlame(
+        `Expected ${String(this.#received)}${this.#maybeNotLabel()} to throw`,
+      ).blameToPreviousFrame();
+    }
+  }
+
+  toHaveBeenCalled(): void {
+    const mock = this.#requireMock();
+    const pass = mock.calls.length > 0;
+    if (!this.#isExpectedResult(pass)) {
+      throw new ErrorWithCustomBlame(
+        `Expected ${String(this.#received)}${this.#maybeNotLabel()} to have been called, but it was${this.#isNot ? '' : "n't"}`,
+      ).blameToPreviousFrame();
+    }
+  }
+
+  toHaveBeenCalledTimes(times: number): void {
+    const mock = this.#requireMock();
+    const pass = mock.calls.length === times;
+    if (!this.#isExpectedResult(pass)) {
+      throw new ErrorWithCustomBlame(
+        `Expected ${String(this.#received)}${this.#maybeNotLabel()} to have been called ${times} times, but it was called ${mock.calls.length} times`,
+      ).blameToPreviousFrame();
+    }
+  }
+
+  toBeGreaterThanOrEqual(expected: number): void {
+    if (typeof this.#received !== 'number') {
+      throw new ErrorWithCustomBlame(
+        `Expected ${String(this.#received)} to be a number but it was a ${typeof this.#received}`,
+      ).blameToPreviousFrame();
+    }
+
+    if (typeof expected !== 'number') {
+      throw new ErrorWithCustomBlame(
+        `Expected ${String(expected)} to be a number but it was a ${typeof expected}`,
+      ).blameToPreviousFrame();
+    }
+
+    const pass = this.#received >= expected;
+    if (!this.#isExpectedResult(pass)) {
+      throw new ErrorWithCustomBlame(
+        `Expected ${String(this.#received)}${this.#maybeNotLabel()} to be greater than or equal to ${expected}`,
+      ).blameToPreviousFrame();
+    }
+  }
+
+  toBeLessThanOrEqual(expected: number): void {
+    if (typeof this.#received !== 'number') {
+      throw new ErrorWithCustomBlame(
+        `Expected ${String(this.#received)} to be a number but it was a ${typeof this.#received}`,
+      ).blameToPreviousFrame();
+    }
+
+    if (typeof expected !== 'number') {
+      throw new ErrorWithCustomBlame(
+        `Expected ${String(expected)} to be a number but it was a ${typeof expected}`,
+      ).blameToPreviousFrame();
+    }
+
+    const pass = this.#received <= expected;
+    if (!this.#isExpectedResult(pass)) {
+      throw new ErrorWithCustomBlame(
+        `Expected ${String(this.#received)}${this.#maybeNotLabel()} to be less than or equal to ${expected}`,
+      ).blameToPreviousFrame();
+    }
+  }
+
+  #isExpectedResult(pass: boolean): boolean {
+    return this.#isNot ? !pass : pass;
+  }
+
+  #maybeNotLabel(): string {
+    return this.#isNot ? ' not' : '';
+  }
+
+  #requireMock(): JestMockFn<Array<mixed>, mixed>['mock'] {
+    try {
+      return ensureMockFunction(this.#received).mock;
+    } catch (error) {
+      const errorWithCustomBlame = ErrorWithCustomBlame.fromError(error);
+      errorWithCustomBlame.message = `Expected ${String(this.#received)} to be a mock function, but it wasn't`;
+      errorWithCustomBlame
+        .blameToPreviousFrame() // ignore `ensureMockFunction`
+        .blameToPreviousFrame() // ignore `requireMock`
+        .blameToPreviousFrame(); // ignore `expect().[method]`
+      throw errorWithCustomBlame;
+    }
+  }
+}
+
+const expect: mixed => Expect = (received: mixed) => new Expect(received);
+
+export default expect;

jest/integration/runtime/mocks.js

@@ -0,0 +1,83 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+export const MOCK_FN_TAG: symbol = Symbol('mock function');
+
+// The type is defined this way because if we get a mixed value, we return
+// a generic mock function, and if we get a typed function, we get a typed mock.
+export const ensureMockFunction: (<TArgs: Array<mixed>, TReturn>(
+  fn: (...TArgs) => TReturn,
+) => JestMockFn<TArgs, TReturn>) &
+  ((fn: mixed) => JestMockFn<Array<mixed>, mixed>) = fn => {
+  // $FlowExpectedError[invalid-computed-prop]
+  // $FlowExpectedError[incompatible-use]
+  if (typeof fn !== 'function' || !fn[MOCK_FN_TAG]) {
+    throw new Error(
+      `Expected ${String(fn)} to be a mock function, but it wasn't`,
+    );
+  }
+
+  // $FlowExpectedError[incompatible-type]
+  // $FlowExpectedError[prop-missing]
+  return fn;
+};
+
+export function createMockFunction<TArgs: Array<mixed>, TReturn>(
+  initialImplementation?: (...TArgs) => TReturn,
+): JestMockFn<TArgs, TReturn> {
+  let implementation: ?(...TArgs) => TReturn = initialImplementation;
+
+  const mock: JestMockFn<TArgs, TReturn>['mock'] = {
+    calls: [],
+    // $FlowExpectedError[incompatible-type]
+    lastCall: undefined,
+    instances: [],
+    contexts: [],
+    results: [],
+  };
+
+  const mockFunction = function (this: mixed, ...args: TArgs): TReturn {
+    let result: JestMockFn<TArgs, TReturn>['mock']['results'][number] = {
+      isThrow: false,
+      // $FlowExpectedError[incompatible-type]
+      value: undefined,
+    };
+
+    if (implementation != null) {
+      try {
+        result.value = implementation.apply(this, args);
+      } catch (error) {
+        result.isThrow = true;
+        result.value = error;
+      }
+    }
+
+    mock.calls.push(args);
+    mock.lastCall = args;
+    // $FlowExpectedError[incompatible-call]
+    mock.instances.push(new.target ? this : undefined);
+    mock.contexts.push(this);
+    mock.results.push(result);
+
+    if (result.isThrow) {
+      throw result.value;
+    }
+
+    return result.value;
+  };
+
+  mockFunction.mock = mock;
+  // $FlowExpectedError[invalid-computed-prop]
+  mockFunction[MOCK_FN_TAG] = true;
+
+  // $FlowExpectedError[prop-missing]
+  return mockFunction;
+}