Mock free functions

README.md

@@ -91,6 +91,18 @@ Syntax is the same as with getter values.
 
 Please note, that stubbing properties that don't have getters only works if [Proxy](http://www.ecma-international.org/ecma-262/6.0/#sec-proxy-objects) object is available (ES6).
 
+### Mocking free functions
+
+Sometimes you need to mock a function, not an object, for example to pass as a callback somewhere. This can be done using `fnmock()`. It works just like any other mock, except it's a function, not an object.
+
+```typescript
+let fn: (a: number, b: string) => number = fnmock();
+when(fn(10, 'hello')).thenReturn(5);
+
+instance(fn)(10, 'hello'); // returns 5
+verify(fn(10, 'hello')).called();
+```
+
 ### Call count verification
 
 ``` typescript

package.json

@@ -50,7 +50,7 @@
     "ts-helpers": "^1.1.2",
     "ts-jest": "^23.0.1",
     "tslint": "^5.7.0",
-    "typescript": "^2.7.2"
+    "typescript": "^3.4.5"
   },
   "dependencies": {
     "lodash": "^4.17.5"

src/Mock.ts

@@ -175,7 +175,7 @@ export class Mocker {
     }
 
     private createMethodToStub(key: string): () => any {
-        return (...args) => {
+        return (...args: any[]) => {
             if (!this.methodStubCollections[key]) {
                 this.methodStubCollections[key] = new MethodStubCollection();
             }

src/ts-mockito.ts

@@ -36,6 +36,17 @@ export function mock<T>(clazz: (new(...args: any[]) => T) | (Function & { protot
     return new Mocker(clazz).getMock();
 }
 
+export function fnmock<R, T extends any[]>(): (...args: T) => R {
+    class Mock {
+        public fn(...args: T): R { return null as R; }
+    }
+
+    const m: Mock = mock(Mock);
+    (m.fn as any).__tsmockitoInstance = instance(m).fn;
+    (m.fn as any).__tsmockitoMocker = (m as any).__tsmockitoMocker;
+    return m.fn;
+}
+
 export function verify<T>(method: T): MethodStubVerificator<T> {
     return new MethodStubVerificator(method as any);
 }
@@ -127,6 +138,7 @@ export function objectContaining(expectedValue: Object): any {
 export default {
     spy,
     mock,
+    fnmock,
     verify,
     when,
     instance,

test/mocking.functions.spec.ts

@@ -0,0 +1,51 @@
+import { capture, fnmock, instance, reset, resetCalls, verify, when } from "../src/ts-mockito";
+
+describe("mocking", () => {
+    describe("mocking functions", () => {
+        it("should mock free functions", () => {
+            const fn: () => number = fnmock();
+
+            when(fn()).thenReturn(1);
+
+            expect(instance(fn)()).toEqual(1);
+            verify(fn()).called();
+        });
+
+        it("should match arguments of free functions", () => {
+            const fn: (a: string, b: number) => number = fnmock();
+
+            when(fn("a", 1)).thenReturn(1);
+
+            expect(instance(fn)("a", 1)).toEqual(1);
+            expect(instance(fn)("a", 2)).toBeNull();
+            verify(fn("a", 1)).called();
+        });
+
+        it("should reset mocks", () => {
+            const fn: () => number = fnmock();
+
+            when(fn()).thenReturn(1);
+            expect(instance(fn)()).toEqual(1);
+
+            reset(fn);
+            expect(instance(fn)()).toBeNull();
+        });
+
+        it("should reset calls", () => {
+            const fn: () => number = fnmock();
+
+            instance(fn)();
+            verify(fn()).once();
+
+            resetCalls(fn);
+            verify(fn()).never();
+        });
+
+        it("should capture parameters", () => {
+            const fn: (a: string) => void = fnmock();
+
+            instance(fn)("a");
+            expect(capture(fn).last()).toEqual(["a"]);
+        });
+    });
+});