Add T object and Test method to Mock

This makes is possible to fail the test instead of panicing in case
that the method was called with unexpected arguments.

Fixes #489

mock: change field 'T' to be private field 'test'
mock_test: MockTestingT not using Mock anymore

mock/mock.go

@@ -191,6 +191,10 @@ type Mock struct {
 	// Holds the calls that were made to this mocked object.
 	Calls []Call
 
+	// test is An optional variable that holds the test struct, to be used when an
+	// invalid mock call was made.
+	test TestingT
+
 	// TestData holds any data that might be useful for testing.  Testify ignores
 	// this data completely allowing you to do whatever you like with it.
 	testData objx.Map
@@ -213,6 +217,27 @@ func (m *Mock) TestData() objx.Map {
 	Setting expectations
 */
 
+// Test sets the test struct variable of the mock object
+func (m *Mock) Test(t TestingT) {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+	m.test = t
+}
+
+// fail fails the current test with the given formatted format and args.
+// In case that a test was defined, it uses the test APIs for failing a test,
+// otherwise it uses panic.
+func (m *Mock) fail(format string, args ...interface{}) {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	if m.test == nil {
+		panic(fmt.Sprintf(format, args...))
+	}
+	m.test.Errorf(format, args...)
+	m.test.FailNow()
+}
+
 // On starts a description of an expectation of the specified method
 // being called.
 //
@@ -329,14 +354,14 @@ func (m *Mock) MethodCalled(methodName string, arguments ...interface{}) Argumen
 		m.mutex.Unlock()
 
 		if closestCall != nil {
-			panic(fmt.Sprintf("\n\nmock: Unexpected Method Call\n-----------------------------\n\n%s\n\nThe closest call I have is: \n\n%s\n\n%s\nDiff: %s",
+			m.fail("\n\nmock: Unexpected Method Call\n-----------------------------\n\n%s\n\nThe closest call I have is: \n\n%s\n\n%s\nDiff: %s",
 				callString(methodName, arguments, true),
 				callString(methodName, closestCall.Arguments, true),
 				diffArguments(closestCall.Arguments, arguments),
-				strings.TrimSpace(mismatch)),
+				strings.TrimSpace(mismatch),
 			)
 		} else {
-			panic(fmt.Sprintf("\nassert: mock: I don't know what to return because the method call was unexpected.\n\tEither do Mock.On(\"%s\").Return(...) first, or remove the %s() call.\n\tThis method was unexpected:\n\t\t%s\n\tat: %s", methodName, methodName, callString(methodName, arguments, true), assert.CallerInfo()))
+			m.fail("\nassert: mock: I don't know what to return because the method call was unexpected.\n\tEither do Mock.On(\"%s\").Return(...) first, or remove the %s() call.\n\tThis method was unexpected:\n\t\t%s\n\tat: %s", methodName, methodName, callString(methodName, arguments, true), assert.CallerInfo())
 		}
 	}
 

mock/mock_test.go

@@ -4,12 +4,11 @@ import (
 	"errors"
 	"fmt"
 	"regexp"
+	"runtime"
 	"sync"
 	"testing"
 	"time"
 
-	"runtime"
-
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -93,6 +92,34 @@ func (i *TestExampleImplementation) TheExampleMethodFuncType(fn ExampleFuncType)
 	return args.Error(0)
 }
 
+// MockTestingT mocks a test struct
+type MockTestingT struct {
+	logfCount, errorfCount, failNowCount int
+}
+
+const mockTestingTFailNowCalled = "FailNow was called"
+
+func (m *MockTestingT) Logf(string, ...interface{}) {
+	m.logfCount++
+}
+
+func (m *MockTestingT) Errorf(string, ...interface{}) {
+	m.errorfCount++
+}
+
+// FailNow mocks the FailNow call.
+// It panics in order to mimic the FailNow behavior in the sense that
+// the execution stops.
+// When expecting this method, the call that invokes it should use the following code:
+//
+//     assert.PanicsWithValue(t, mockTestingTFailNowCalled, func() {...})
+func (m *MockTestingT) FailNow() {
+	m.failNowCount++
+
+	// this function should panic now to stop the execution as expected
+	panic(mockTestingTFailNowCalled)
+}
+
 /*
 	Mock
 */
@@ -205,6 +232,34 @@ func Test_Mock_On_WithIntArgMatcher(t *testing.T) {
 	})
 }
 
+func TestMock_WithTest(t *testing.T) {
+	var (
+		mockedService TestExampleImplementation
+		mockedTest    MockTestingT
+	)
+
+	mockedService.Test(&mockedTest)
+	mockedService.On("TheExampleMethod", 1, 2, 3).Return(0, nil)
+
+	// Test that on an expected call, the test was not failed
+
+	mockedService.TheExampleMethod(1, 2, 3)
+
+	// Assert that Errorf and FailNow were not called
+	assert.Equal(t, 0, mockedTest.errorfCount)
+	assert.Equal(t, 0, mockedTest.failNowCount)
+
+	// Test that on unexpected call, the mocked test was called to fail the test
+
+	assert.PanicsWithValue(t, mockTestingTFailNowCalled, func() {
+		mockedService.TheExampleMethod(1, 1, 1)
+	})
+
+	// Assert that Errorf and FailNow were called once
+	assert.Equal(t, 1, mockedTest.errorfCount)
+	assert.Equal(t, 1, mockedTest.failNowCount)
+}
+
 func Test_Mock_On_WithPtrArgMatcher(t *testing.T) {
 	var mockedService TestExampleImplementation