Restructured code and now requires >= Go v1.13 for error handling

In order allow customizations of the golden library per unit test,
the goldie library was restructured to not use global variables
and adopt the function options pattern:

  https://dave.cheney.net/2014/10/17/functional-options-for-friendly-apis

This restructuring also made it easier to implement the following
features:

* Different fixture directories
* A separate directory per unit test
* A separate directory per subtest in the unit test
* Erroring out if a template didn't get data that it needed
* Diff output (classic or in color)
* Using your own diff function for output

Although a little non standard, the methods that a consumer will
be using are now all in the `interface.go` file.

In addition, error handling was cleaned up (now uses pointer
receivers) and leverages the new Go v1.13 `errors` package.

More unit testing is desired.

Author: gtrevg

README.md

@@ -24,6 +24,7 @@ what is present in the golden test file.
 
 ```
 func TestExample(t *testing.T) {
+    g := goldie.New(t)
     recorder := httptest.NewRecorder()
 
     req, err := http.NewRequest("GET", "/example", nil)
@@ -32,14 +33,14 @@ func TestExample(t *testing.T) {
     handler := http.HandlerFunc(ExampleHandler)
     handler.ServeHTTP()
 
-    goldie.Assert(t, "example", recorder.Body.Bytes())
+    g.Assert(t, "example", recorder.Body.Bytes())
 }
 ```
 
 ## Using template golden file
 
 If some values in the golden file can change depending on the test, you can use golang
-template in the golden file and pass the data to `goldie.AssertWithTemplate`.
+template in the golden file and pass the data to `AssertWithTemplate`.
 
 ### example.golden
 ```
@@ -49,6 +50,8 @@ This is a {{ .Type }} file.
 ### Test
 ```
 func TestTemplateExample(t *testing.T) {
+    g := goldie.New(t)
+
     recorder := httptest.NewRecorder()
 
     req, err := http.NewRequest("POST", "/example/Golden", nil)
@@ -63,7 +66,7 @@ func TestTemplateExample(t *testing.T) {
         Type:	"Golden",
     }
 
-    goldie.AssertWithTemplate(t, "example", data, recorder.Body.Bytes())
+    g.AssertWithTemplate(t, "example", data, recorder.Body.Bytes())
 }
 ```
 
@@ -76,14 +79,32 @@ drop the `-update` flag.
 
 `go test ./...`
 
+## Options
+`goldie` supports a number of configuration options that will alter the behavior
+of the library.  These options should be passed into the `goldie.New()` method.
+
+```
+func TestNewExample(t *testing.T) {
+    g := goldie.New(
+        t,
+        goldie.WithFixtureDir("test-fixtures"),
+        goldie.WithNameSuffix(".golden.json"),
+        goldie.WithDiffEngine(goldie.ColoredDiff),
+        goldie.WithTestNameForDir(true),
+    )
+
+    g.Assert(t, "example", "my example data")
+}
+
+```
+
 ## FAQ
 
 ### Do you need any help in the project?
 
 Yes, please! Pull requests are most welcome. On the wish list:
 
 - Unit tests.
-- Better output for failed tests. A diff of some sort would be great.
 
 ### Why the name `goldie`?
 

errors.go

@@ -8,14 +8,15 @@ type errFixtureNotFound struct {
 }
 
 // newErrFixtureNotFound returns a new instance of the error.
-func newErrFixtureNotFound() errFixtureNotFound {
-	return errFixtureNotFound{
+func newErrFixtureNotFound() *errFixtureNotFound {
+	return &errFixtureNotFound{
+		// TODO: flag name should be based on the variable value
 		message: "Golden fixture not found. Try running with -update flag.",
 	}
 }
 
 // Error returns the error message.
-func (e errFixtureNotFound) Error() string {
+func (e *errFixtureNotFound) Error() string {
 	return e.message
 }
 
@@ -26,13 +27,13 @@ type errFixtureMismatch struct {
 }
 
 // newErrFixtureMismatch returns a new instance of the error.
-func newErrFixtureMismatch(message string) errFixtureMismatch {
-	return errFixtureMismatch{
+func newErrFixtureMismatch(message string) *errFixtureMismatch {
+	return &errFixtureMismatch{
 		message: message,
 	}
 }
 
-func (e errFixtureMismatch) Error() string {
+func (e *errFixtureMismatch) Error() string {
 	return e.message
 }
 
@@ -42,12 +43,32 @@ type errFixtureDirectoryIsFile struct {
 }
 
 // newFixtureDirectoryIsFile returns a new instance of the error.
-func newErrFixtureDirectoryIsFile(file string) errFixtureDirectoryIsFile {
-	return errFixtureDirectoryIsFile{
+func newErrFixtureDirectoryIsFile(file string) *errFixtureDirectoryIsFile {
+	return &errFixtureDirectoryIsFile{
 		file: file,
 	}
 }
 
-func (e errFixtureDirectoryIsFile) Error() string {
+func (e *errFixtureDirectoryIsFile) Error() string {
 	return fmt.Sprintf("fixture folder is a file: %s", e.file)
 }
+
+func (e *errFixtureDirectoryIsFile) File() string {
+	return e.file
+}
+
+// errMissingKey is thrown when a value for a template is missing
+type errMissingKey struct {
+	message string
+}
+
+// newErrMissingKey returns a new instance of the error.
+func newErrMissingKey(message string) *errMissingKey {
+	return &errMissingKey{
+		message: message,
+	}
+}
+
+func (e *errMissingKey) Error() string {
+	return e.message
+}

errors_test.go

@@ -11,15 +11,15 @@ func TestErrFixtureNotFound(t *testing.T) {
 	err := newErrFixtureNotFound()
 
 	assert.Equal(t, expected, err.Error())
-	assert.IsType(t, errFixtureNotFound{}, err)
+	assert.IsType(t, &errFixtureNotFound{}, err)
 }
 
 func TestErrFixtureMismatch(t *testing.T) {
 	message := "example message"
 	err := newErrFixtureMismatch(message)
 
 	assert.Equal(t, message, err.Error())
-	assert.IsType(t, errFixtureMismatch{}, err)
+	assert.IsType(t, &errFixtureMismatch{}, err)
 }
 
 func TestErrFixtureDirectoryIsFile(t *testing.T) {
@@ -28,5 +28,5 @@ func TestErrFixtureDirectoryIsFile(t *testing.T) {
 	err := newErrFixtureDirectoryIsFile(location)
 
 	assert.Equal(t, message, err.Error())
-	assert.IsType(t, errFixtureDirectoryIsFile{}, err)
+	assert.IsType(t, &errFixtureDirectoryIsFile{}, err)
 }

go.mod

@@ -2,4 +2,9 @@ module github.com/sebdah/goldie
 
 go 1.12
 
-require github.com/stretchr/testify v1.3.0
+require (
+	github.com/pkg/errors v0.8.1
+	github.com/pmezard/go-difflib v1.0.0
+	github.com/sergi/go-diff v1.0.0
+	github.com/stretchr/testify v1.3.0
+)

go.sum

@@ -1,7 +1,11 @@
 github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pkg/errors v0.8.1 h1:iURUrRGxPUNPdy5/HRSm+Yj6okJ6UtLINN0Q9M4+h3I=
+github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sergi/go-diff v1.0.0 h1:Kpca3qRNrduNnOQeazBd0ysaKrUJiIuISHxogkT9RPQ=
+github.com/sergi/go-diff v1.0.0/go.mod h1:0CfEIISq7TuYL3j771MWULgwwjU+GofnZX9QAmXWZgo=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.3.0 h1:TivCn/peBQ7UY8ooIcPgZFpTNSz0Q2U6UrFlUfqbe0Q=
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=