Merge pull request #264 from stretchr/issue-263

Fix Backwards Incompatible change to TestingT

assert/assertions.go

@@ -21,6 +21,9 @@ import (
 // TestingT is an interface wrapper around *testing.T
 type TestingT interface {
 	Errorf(format string, args ...interface{})
+}
+
+type FailNower interface {
 	FailNow()
 }
 
@@ -185,7 +188,18 @@ func indentMessageLines(message string, tabs int) string {
 // FailNow fails test
 func FailNow(t TestingT, failureMessage string, msgAndArgs ...interface{}) bool {
 	Fail(t, failureMessage, msgAndArgs...)
-	t.FailNow()
+
+	// We cannot extend TestingT with FailNow() and
+	// maintain backwards compatibility, so we fallback
+	// to panicking when FailNow is not available in
+	// TestingT.
+	// See issue #263
+
+	if t, ok := t.(FailNower); ok {
+		t.FailNow()
+	} else {
+		panic("test failed and t is missing `FailNow()`")
+	}
 	return false
 }
 

assert/assertions_test.go

@@ -1090,3 +1090,31 @@ func TestDiffEmptyCases(t *testing.T) {
 	Equal(t, "", diff(1, 2))
 	Equal(t, "", diff([]int{1}, []bool{true}))
 }
+
+type mockTestingT struct {
+}
+
+func (m *mockTestingT) Errorf(format string, args ...interface{}) {}
+
+func TestFailNowWithPlainTestingT(t *testing.T) {
+	mockT := &mockTestingT{}
+
+	Panics(t, func() {
+		FailNow(mockT, "failed")
+	}, "should panic since mockT is missing FailNow()")
+}
+
+type mockFailNowTestingT struct {
+}
+
+func (m *mockFailNowTestingT) Errorf(format string, args ...interface{}) {}
+
+func (m *mockFailNowTestingT) FailNow() {}
+
+func TestFailNowWithFullTestingT(t *testing.T) {
+	mockT := &mockFailNowTestingT{}
+
+	NotPanics(t, func() {
+		FailNow(mockT, "failed")
+	}, "should call mockT.FailNow() rather than panicking")
+}