mock: add OnF method

mock/mock.go

@@ -207,6 +207,22 @@ func (c *Call) On(methodName string, arguments ...interface{}) *Call {
 	return c.Parent.On(methodName, arguments...)
 }
 
+// OnF chains a new expectation description onto the mcked interface using
+// a function reference instead of a string method name.
+// for example:
+//
+//	mock.
+//	   OnF(mocked.MyMethod, 1).Return(nil).
+//	   OnF(mocked.MyOtherMethod, 'a', 'b', 'c').Return(errors.New("Some Error"))
+//
+// The `method` argument must be a function; otherwise, this call will panic.
+// The function name is resolved using reflection and runtime information.
+//
+//go:noinline
+func (c *Call) OnF(method interface{}, args ...interface{}) *Call {
+	return c.Parent.On(runtimeMethodName(method), args...)
+}
+
 // Unset removes all mock handlers that satisfy the call instance arguments from being
 // called. Only supported on call instances with static input arguments.
 //
@@ -380,6 +396,18 @@ func (m *Mock) On(methodName string, arguments ...interface{}) *Call {
 	return c
 }
 
+// OnF starts a description of an expectation of the specified method
+// being called using a function reference instead of a string method name.
+//
+//	Mock.OnF(mocked.MyMethod, arg1, arg2)
+//
+// The `method` argument must be a function; otherwise, OnF will panic.
+// The function name is determined using reflection and runtime information,
+// and then passed to On(methodName, args...).
+func (m *Mock) OnF(method interface{}, args ...interface{}) *Call {
+	return m.On(runtimeMethodName(method), args...)
+}
+
 // /*
 // 	Recording and responding to activity
 // */
@@ -1303,6 +1331,20 @@ func funcName(f *runtime.Func) string {
 	return splitted[len(splitted)-1]
 }
 
+func runtimeMethodName(f interface{}) string {
+	t := reflect.TypeOf(f)
+
+	if t.Kind() != reflect.Func {
+		panic("not a function")
+	}
+
+	fname := runtime.FuncForPC(reflect.ValueOf(f).Pointer()).Name()
+
+	parts := strings.Split(fname, ".")
+
+	return strings.Split(parts[len(parts)-1], "-")[0]
+}
+
 func isFuncSame(f1, f2 *runtime.Func) bool {
 	f1File, f1Loc := f1.FileLine(f1.Entry())
 	f2File, f2Loc := f2.FileLine(f2.Entry())

mock/mock_test.go

@@ -558,6 +558,17 @@ func Test_Mock_On_WithFuncTypeArg(t *testing.T) {
 	})
 }
 
+func Test_Mock_OnF(t *testing.T) {
+	t.Parallel()
+
+	// make a test impl object
+	var mockedService = new(TestExampleImplementation)
+
+	c := mockedService.OnF(mockedService.TheExampleMethod)
+	assert.Equal(t, []*Call{c}, mockedService.ExpectedCalls)
+	assert.Equal(t, "TheExampleMethod", c.Method)
+}
+
 func Test_Mock_Unset(t *testing.T) {
 	t.Parallel()