❤️ return empty if not get diff

README.md

@@ -5,11 +5,46 @@
 [![test](https://github.com/budougumi0617/cmpmock/workflows/test/badge.svg)](https://github.com/budougumi0617/cmpmock/actions?query=workflow%3Atest)
 [![reviewdog](https://github.com/budougumi0617/cmpmock/workflows/reviewdog/badge.svg)](https://github.com/budougumi0617/cmpmock/actions?query=workflow%3Areviewdog)
 
+Readable & Flexible matcher for https://github.com/golang/mock
+
 ## Description
 
 
+
+### Readable ouput
+
+Default output
+```
+expected call at /Users/budougumi0617/go/src/github.com/budougumi0617/cmpmock/_example/repo_test.go:26 doesn't match the argument at index 1.
+Got: &{John Due Tokyo 2021-04-23 02:46:58.145696 +0900 JST m=+0.000595005}
+Want: is equal to &{John Due Tokyo 2021-04-23 02:46:48.145646 +0900 JST m=-9.999455563}
+```
+
+use `cmpmock.DiffEq`
+```
+expected call at /Users/budougumi0617/go/src/github.com/budougumi0617/cmpmock/_example/repo_test.go:27 doesn't match the argument at index 1.
+Got: &{John Due Tokyo 2021-04-23 02:46:33.290458 +0900 JST m=+0.001035665}
+Want: diff(-got +want) is   &_example.User{
+ 	Name:     "John Due",
+ 	Address:  "Tokyo",
+- 	CreateAt: s"2021-04-23 02:46:33.290458 +0900 JST m=+0.001035665",
++ 	CreateAt: s"2021-04-23 02:46:23.290383 +0900 JST m=-9.999039004",
+}
+```
+
 ## Usage
 
+```go
+wantUser := &_example.User{
+	Name:     name,
+	Address:  address,
+	CreateAt: time.Now().Add(-10 * time.Second),
+}
+
+mrepo := mock_example.NewMockUserRepo(ctrl)
+mrepo.EXPECT().Save(ctx, cmpmock.DiffEq(wantUser)).Return(nil)
+```
+
 ## Installation
 
 ```bash

diffmatcher.go

@@ -31,5 +31,8 @@ func (d *diffMatcher) Matches(x interface{}) bool {
 }
 
 func (d *diffMatcher) String() string {
+	if d.diff == "" {
+		return ""
+	}
 	return fmt.Sprintf("diff(-got +want) is %s", d.diff)
 }

diffmatcher_test.go

@@ -1,7 +1,6 @@
 package cmpmock
 
 import (
-	"fmt"
 	"testing"
 	"time"
 
@@ -12,7 +11,6 @@ func Test_DiffEq(t *testing.T) {
 	type Foo struct{ CreateAt time.Time }
 	t1 := time.Now()
 	t2 := t1.Add(100 * time.Millisecond)
-	defaultString := "diff(-got +want) is %s"
 	type args struct {
 		want interface{}
 		opts cmp.Options
@@ -42,7 +40,7 @@ func Test_DiffEq(t *testing.T) {
 			if got := sut.Matches(x); got != tt.wantMatch {
 				t.Errorf("Matches() = %v, want %v", got, tt.wantMatch)
 			}
-			if got := sut.String(); got != fmt.Sprintf(defaultString, tt.wantDiff) {
+			if got := sut.String(); got != tt.wantDiff {
 				t.Errorf("String() = %q, want %q", got, tt.wantDiff)
 			}
 		})