Add Mock.Of<F> type (#141)

Author: hasparus

.changeset/happy-apples-impress.md

@@ -0,0 +1,5 @@
+---
+'earljs': patch
+---
+
+Function mocks can now be typed as Mock.Of<TFunctionType>

package.json

@@ -34,6 +34,7 @@
     "chai": "^4.2.0",
     "chai-as-promised": "^7.1.1",
     "cross-spawn-with-kill": "^1.0.0",
+    "conditional-type-checks": "^1.0.5",
     "eslint": "^7.29.0",
     "eslint-config-typestrict": "^1.0.2",
     "eslint-plugin-import": "^2.23.4",

packages/docs/guides/mocks.md

@@ -15,6 +15,7 @@ To create a mock do:
 ```typescript
 import { mockFn } from 'earljs'
 
+// mock: Mock<[number, number], number>
 const mock = mockFn<[number, number], number>()
 ```
 
@@ -25,6 +26,7 @@ that's why you need to pass type arguments between angle brackets `<`, `>`.
 Alternatively, you can pass function type as a type argument:
 
 ```typescript
+// mock: Mock.Of<(a: number, b: number) => number>
 const mock = mockFn<(a: number, b: number) => number>()
 ```
 

packages/earljs/src/mocks/mockFn.ts

@@ -38,9 +38,7 @@ interface Override {
   spec: Spec
 }
 
-export function mockFn<FUNCTION_SIG extends (...args: any) => any>(
-  defaultImpl?: FUNCTION_SIG,
-): Mock<Parameters<FUNCTION_SIG>, ReturnType<FUNCTION_SIG>>
+export function mockFn<FUNCTION_SIG extends (...args: any) => any>(defaultImpl?: FUNCTION_SIG): Mock.Of<FUNCTION_SIG>
 export function mockFn<ARGS extends any[], RETURN = any>(defaultImpl?: (...args: ARGS) => RETURN): Mock<ARGS, RETURN>
 export function mockFn<ARGS extends any[], RETURN = any>(defaultImpl?: (...args: ARGS) => RETURN): Mock<ARGS, RETURN> {
   let spec: Spec = {

packages/earljs/src/mocks/types.ts

@@ -1,20 +1,20 @@
-export interface MockCall<ARGS, RETURN> {
-  args: ARGS
-  result: { type: 'return'; value: RETURN } | { type: 'throw'; error: any }
+export interface MockCall<TArgs, TReturn> {
+  args: TArgs
+  result: { type: 'return'; value: TReturn } | { type: 'throw'; error: any }
 }
 
 export type Awaited<T> = T extends PromiseLike<infer PT> ? PT : never
 
-export interface Mock<ARGS extends any[], RETURN> {
+export interface Mock<TArgs extends any[], TReturn> {
   /**
    * Calls the mock function.
    */
-  (...args: ARGS): RETURN
+  (...args: TArgs): TReturn
 
   /**
    * An array containing all the performed calls.
    */
-  calls: MockCall<ARGS, RETURN>[]
+  calls: MockCall<TArgs, TReturn>[]
 
   /**
    * Checks if all the expected calls to the mock have been performed.
@@ -26,106 +26,110 @@ export interface Mock<ARGS extends any[], RETURN> {
    * Overrides any previous configuration.
    * @param value value to be returned.
    */
-  returns(value: RETURN): Mock<ARGS, RETURN>
+  returns(value: TReturn): Mock<TArgs, TReturn>
   /**
    * Schedules the mock to return a value the next time it's called.
    * If anything is already scheduled it will be used first.
    * @param value value to be returned.
    */
-  returnsOnce(value: RETURN): Mock<ARGS, RETURN>
+  returnsOnce(value: TReturn): Mock<TArgs, TReturn>
 
   /**
    * Sets the error thrown by calls to the Mock.
    * Overrides any previous configuration.
    * @param error error to be thrown.
    */
-  throws(error: any): Mock<ARGS, RETURN>
+  throws(error: any): Mock<TArgs, TReturn>
   /**
    * Schedules the mock to throw an error the next time it's called.
    * If anything is already scheduled it will be used first.
    * @param error error to be thrown.
    */
-  throwsOnce(error: any): Mock<ARGS, RETURN>
+  throwsOnce(error: any): Mock<TArgs, TReturn>
 
   /**
    * Sets the underlying implementation of the Mock.
    * Overrides any previous configuration.
    * @param implementation function to execute.
    */
-  executes(implementation: (...args: ARGS[]) => RETURN): Mock<ARGS, RETURN>
+  executes(implementation: (...args: TArgs[]) => TReturn): Mock<TArgs, TReturn>
   /**
    * Schedules the mock to use the provided implementation the next time it's called.
    * If anything is already scheduled it will be used first.
    * @param implementation function to execute.
    */
-  executesOnce(implementation: (...args: ARGS[]) => RETURN): Mock<ARGS, RETURN>
+  executesOnce(implementation: (...args: TArgs[]) => TReturn): Mock<TArgs, TReturn>
 
   /**
    * Sets the return value wrapped in Promise.resolve of calls to the Mock.
    * @param value value to be returned.
    */
-  resolvesTo(value: Awaited<RETURN>): Mock<ARGS, RETURN>
+  resolvesTo(value: Awaited<TReturn>): Mock<TArgs, TReturn>
   /**
    * Schedules the mock to return value wrapped in Promise.resolve the next time it's called.
    * If anything is already scheduled it will be used first.
    * @param value value to be returned.
    */
-  resolvesToOnce(value: Awaited<RETURN>): Mock<ARGS, RETURN>
+  resolvesToOnce(value: Awaited<TReturn>): Mock<TArgs, TReturn>
 
   /**
    * Sets the error rejected by calls to the Mock.
    * @param error error to be thrown.
    */
-  rejectsWith(error: any): Mock<ARGS, RETURN>
+  rejectsWith(error: any): Mock<TArgs, TReturn>
   /**
    * Schedules the mock to reject with value the next time it's called.
    * If anything is already scheduled it will be used first.
    * @param error error to be thrown.
    */
-  rejectsWithOnce(error: any): Mock<ARGS, any>
+  rejectsWithOnce(error: any): Mock<TArgs, any>
 
   /**
    * Specifies a different behavior when other arguments are given
    * @param args arguments to match
    */
-  given<B extends ARGS>(
+  given<B extends TArgs>(
     ...args: B
   ): {
     /**
      * Schedules the mock to return a value the next time it's called.
      * If anything is already scheduled it will be used first.
      * @param value value to be returned.
      */
-    returnsOnce(value: RETURN): Mock<ARGS, RETURN>
+    returnsOnce(value: TReturn): Mock<TArgs, TReturn>
 
     /**
      * Schedules the mock to throw an error the next time it's called.
      * If anything is already scheduled it will be used first.
      * @param error error to be thrown.
      */
-    throwsOnce(error: any): Mock<ARGS, RETURN>
+    throwsOnce(error: any): Mock<TArgs, TReturn>
 
     /**
      * Schedules the mock use the provided implementation the next time it's called.
      * If anything is already scheduled it will be used first.
      * @param implementation function to execute.
      */
-    executesOnce(implementation: (...args: B) => RETURN): Mock<ARGS, RETURN>
+    executesOnce(implementation: (...args: B) => TReturn): Mock<TArgs, TReturn>
 
     /**
      * Schedules the mock to return value wrapped in Promise.resolve the next time it's called.
      * If anything is already scheduled it will be used first.
      * @param value value to be returned.
      */
-    resolvesToOnce(value: Awaited<RETURN>): Mock<ARGS, RETURN>
+    resolvesToOnce(value: Awaited<TReturn>): Mock<TArgs, TReturn>
 
     /**
      * Schedules the mock to reject with value the next time it's called.
      * If anything is already scheduled it will be used first.
      * @param error error to be thrown.
      */
-    rejectsWithOnce(error: any): Mock<ARGS, RETURN>
+    rejectsWithOnce(error: any): Mock<TArgs, TReturn>
   }
 }
 
-export type MockArgs<T> = T extends Mock<infer ARGS, any> ? ARGS : never
+export type MockArgs<T> = T extends Mock<infer Args, any> ? Args : never
+
+export declare namespace Mock {
+  export type Of<T extends (...args: any[]) => any> = Mock<Parameters<T>, ReturnType<T>>
+}

packages/earljs/test/mocks/mockFn.test.ts

@@ -1,7 +1,8 @@
 import { expect } from 'chai'
+import { AssertTrue, IsExact } from 'conditional-type-checks'
 
 import { expect as earl } from '../../src'
-import { mockFn, MockNotConfiguredError } from '../../src/mocks'
+import { Mock, mockFn, MockNotConfiguredError } from '../../src/mocks'
 import { noop } from '../common'
 
 const sum = (a: number, b: number) => a + b
@@ -135,6 +136,15 @@ describe('Mock', () => {
 
       expect(fn(2, 2)).to.eq(4)
     })
+
+    it('infers types correctly with functional generic parameter', () => {
+      type Operation = (a: number, b: number) => number
+      const fn = mockFn<Operation>((a, b) => a + b)
+
+      expect(fn(2, 2)).to.eq(4)
+
+      type _ = AssertTrue<IsExact<Mock<[number, number], number>, Mock.Of<Operation>>>
+    })
   })
 
   describe('.executesOnce', () => {

yarn.lock

@@ -4579,6 +4579,11 @@ concordance@^4.0.0:
     semver "^5.5.1"
     well-known-symbols "^2.0.0"
 
+conditional-type-checks@^1.0.5:
+  version "1.0.5"
+  resolved "https://registry.yarnpkg.com/conditional-type-checks/-/conditional-type-checks-1.0.5.tgz#310ecd13c46c3963fbe9a2f8f93511d88cdcc973"
+  integrity sha512-DkfkvmjXVe4ye4llJ1JADtO3dNvqqcQM08cA9BhNt9Oe8pyRW8X1CZyBg9Qst05bDV9BJM01KLmnFh78NcJgNg==
+
 config-chain@^1.1.11:
   version "1.1.12"
   resolved "https://registry.yarnpkg.com/config-chain/-/config-chain-1.1.12.tgz#0fde8d091200eb5e808caf25fe618c02f48e4efa"