feat(jest-when): types for jest-when at https://github.com/timkindberg/jest-when (#28773)

types/jest-when/index.d.ts

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+// Type definitions for jest-when 1.1
+// Project: https://github.com/timkindberg/jest-when#readme
+// Definitions by: Alden Taylor <https://github.com/aldentaylor>
+// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+// TypeScript Version: 2.3
+
+/// <reference types="jest" />
+
+export interface PartialMockInstance<T> {
+  mockReturnValue: jest.MockInstance<T>['mockReturnValue'];
+}
+
+export interface When {
+  <T>(fn: jest.Mocked<T> | jest.Mock<T>): When;
+  // due to no-unnecessary-generics lint rule, the generics have been replaced with 'any'
+  // calledWith<T>(...matchers: any[]): PartialMockInstance<T>;
+  // expectCalledWith<T>(...matchers: any[]): PartialMockInstance<T>;
+  calledWith(...matchers: any[]): PartialMockInstance<any>;
+  expectCalledWith(...matchers: any[]): PartialMockInstance<any>;
+}
+
+export const when: When;

types/jest-when/jest-when-tests.ts

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+import { when } from 'jest-when';
+
+describe('mock-when test', () => {
+  it('basic usage:', () => {
+    const fn = jest.fn();
+    when(fn).calledWith(1).mockReturnValue('yay!');
+
+    const result = fn(1);
+    expect(result).toEqual('yay!');
+  });
+
+  it('Supports multiple args:', () => {
+    const fn = jest.fn();
+    when(fn).calledWith(1, true, 'foo').mockReturnValue('yay!');
+
+    const result = fn(1, true, 'foo');
+    expect(result).toEqual('yay!');
+  });
+
+  it('Supports jest matchers:', () => {
+    const fn = jest.fn();
+    when(fn).calledWith(
+      expect.anything(),
+      expect.any(Number),
+      expect.arrayContaining([false])
+    ).mockReturnValue('yay!');
+
+    const result = fn('whatever', 100, [true, false]);
+    expect(result).toEqual('yay!');
+  });
+
+  it('Supports compound declarations:', () => {
+    const fn = jest.fn();
+    when(fn).calledWith(1).mockReturnValue('no');
+    when(fn).calledWith(2).mockReturnValue('way?');
+    when(fn).calledWith(3).mockReturnValue('yes');
+    when(fn).calledWith(4).mockReturnValue('way!');
+
+    expect(fn(1)).toEqual('no');
+    expect(fn(2)).toEqual('way?');
+    expect(fn(3)).toEqual('yes');
+    expect(fn(4)).toEqual('way!');
+    expect(fn(5)).toEqual(undefined);
+  });
+
+  it('Assert the args:', () => {
+    const fn = jest.fn();
+    when(fn).expectCalledWith(1).mockReturnValue('x');
+    let testPassed = false;
+    try {
+      fn(2); // Will throw a helpful jest assertion error with args diff
+    } catch (e) {
+      testPassed = true;
+    }
+    expect(testPassed).toBeTruthy();
+  });
+});

types/jest-when/tsconfig.json

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+{
+  "compilerOptions": {
+    "module": "commonjs",
+    "lib": [
+      "es6"
+    ],
+    "noImplicitAny": true,
+    "noImplicitThis": true,
+    "strictNullChecks": true,
+    "strictFunctionTypes": true,
+    "baseUrl": "../",
+    "typeRoots": [
+      "../"
+    ],
+    "types": [],
+    "noEmit": true,
+    "forceConsistentCasingInFileNames": true
+  },
+  "files": [
+    "index.d.ts",
+    "jest-when-tests.ts"
+  ]
+}

types/jest-when/tslint.json

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+{ "extends": "dtslint/dt.json" }