Add an option to disabled usage of stringer methods.

This is especially annoying for snapshotting custom errors that contain
some payload. The payload would arbitrary be dismissed which is
confusing.

fixes #45

config.go

@@ -76,6 +76,15 @@ func SnapshotFileExtension(snapshotFileExtension string) Configurator {
 	}
 }
 
+// UseStringerMethods invoke String() or Error() methods when available rather than dumping the object.
+// This should probably be disabled by default but is not for backwards compatibility reasons.
+// Default: true
+func UseStringerMethods(useStringerMethods bool) Configurator {
+	return func(c *Config) {
+		c.useStringerMethods = useStringerMethods
+	}
+}
+
 // Config provides the same snapshotting functions with additional configuration capabilities.
 type Config struct {
 	shouldUpdate           func() bool
@@ -84,6 +93,7 @@ type Config struct {
 	createNewAutomatically bool
 	fatalOnMismatch        bool
 	snapshotFileExtension  string
+	useStringerMethods     bool
 }
 
 // NewDefaultConfig returns a new Config instance initialised with the same options as
@@ -96,6 +106,7 @@ func NewDefaultConfig() *Config {
 		CreateNewAutomatically(true),
 		FatalOnMismatch(false),
 		SnapshotFileExtension(""),
+		UseStringerMethods(true),
 	)
 }
 
@@ -110,5 +121,6 @@ func (c *Config) clone() *Config {
 		createNewAutomatically: c.createNewAutomatically,
 		fatalOnMismatch:        c.fatalOnMismatch,
 		snapshotFileExtension:  c.snapshotFileExtension,
+		useStringerMethods:     c.useStringerMethods,
 	}
 }

cupaloy.go

@@ -98,7 +98,7 @@ func (c *Config) WithOptions(configurators ...Configurator) *Config {
 }
 
 func (c *Config) snapshot(snapshotName string, i ...interface{}) error {
-	snapshot := takeSnapshot(i...)
+	snapshot := c.takeSnapshot(i...)
 
 	prevSnapshot, err := c.readSnapshot(snapshotName)
 	if os.IsNotExist(err) {
@@ -111,7 +111,7 @@ func (c *Config) snapshot(snapshotName string, i ...interface{}) error {
 		return err
 	}
 
-	if snapshot == prevSnapshot || takeV1Snapshot(i...) == prevSnapshot {
+	if snapshot == prevSnapshot || c.takeV1Snapshot(i...) == prevSnapshot {
 		// previous snapshot matches current value
 		return nil
 	}

examples/.snapshots/TestUseStringerMethods-disabled

@@ -0,0 +1,2 @@
+(examples_test.stringer) {
+}

examples/.snapshots/TestUseStringerMethods-enabled

@@ -0,0 +1 @@
+(examples_test.stringer) with stringer

examples/advanced_test.go

@@ -2,11 +2,12 @@ package examples_test
 
 import (
 	"bytes"
-	"github.com/bradleyjkemp/cupaloy/v2/internal"
 	"io/ioutil"
 	"strings"
 	"testing"
 
+	"github.com/bradleyjkemp/cupaloy/v2/internal"
+
 	"github.com/bradleyjkemp/cupaloy/v2"
 	"github.com/stretchr/testify/mock"
 )
@@ -65,7 +66,6 @@ func TestUpdate(t *testing.T) {
 		t.Fatalf("Error returned will be of type ErrSnapshotUpdated")
 	}
 
-
 }
 
 // If a snapshot doesn't exist then it is created and an error returned
@@ -209,3 +209,22 @@ func TestSnapshotFileExtension(t *testing.T) {
 	snapshotter := cupaloy.New(cupaloy.SnapshotFileExtension(".myextension"))
 	snapshotter.SnapshotT(t, "This should end up in a file with extension .myextension")
 }
+
+type stringer struct {
+}
+
+func (s stringer) String() string {
+	return "with stringer"
+}
+
+func TestUseStringerMethods(t *testing.T) {
+	s := stringer{}
+
+	t.Run("enabled", func(t *testing.T) {
+		cupaloy.New(cupaloy.UseStringerMethods(true)).SnapshotT(t, s)
+	})
+
+	t.Run("disabled", func(t *testing.T) {
+		cupaloy.New(cupaloy.UseStringerMethods(false)).SnapshotT(t, s)
+	})
+}

util.go

@@ -15,14 +15,6 @@ import (
 	"github.com/pmezard/go-difflib/difflib"
 )
 
-var spewConfig = spew.ConfigState{
-	Indent:                  "  ",
-	SortKeys:                true, // maps should be spewed in a deterministic order
-	DisablePointerAddresses: true, // don't spew the addresses of pointers
-	DisableCapacities:       true, // don't spew capacities of collections
-	SpewKeys:                true, // if unable to sort map keys then spew keys to strings and sort those
-}
-
 //go:generate $GOPATH/bin/mockery -output=examples -outpkg=examples_test -testonly -name=TestingT
 
 // TestingT is a subset of the interface testing.TB allowing it to be mocked in tests.
@@ -47,17 +39,28 @@ func envVariableSet(envVariable string) bool {
 	return varSet
 }
 
+func (c *Config) getSpewConfig() *spew.ConfigState {
+	return &spew.ConfigState{
+		Indent:                  "  ",
+		SortKeys:                true, // maps should be spewed in a deterministic order
+		DisablePointerAddresses: true, // don't spew the addresses of pointers
+		DisableCapacities:       true, // don't spew capacities of collections
+		SpewKeys:                true, // if unable to sort map keys then spew keys to strings and sort those
+		DisableMethods:          !c.useStringerMethods,
+	}
+}
+
 func (c *Config) snapshotFilePath(testName string) string {
 	return filepath.Join(c.subDirName, testName+c.snapshotFileExtension)
 }
 
 // Legacy snapshot format where all items were spewed
-func takeV1Snapshot(i ...interface{}) string {
-	return spewConfig.Sdump(i...)
+func (c *Config) takeV1Snapshot(i ...interface{}) string {
+	return c.getSpewConfig().Sdump(i...)
 }
 
 // New snapshot format where some types are written out raw to the file
-func takeSnapshot(i ...interface{}) string {
+func (c *Config) takeSnapshot(i ...interface{}) string {
 	snapshot := &bytes.Buffer{}
 	for _, v := range i {
 		switch vt := v.(type) {
@@ -68,7 +71,7 @@ func takeSnapshot(i ...interface{}) string {
 			snapshot.Write(vt)
 			snapshot.WriteString("\n")
 		default:
-			spewConfig.Fdump(snapshot, v)
+			c.getSpewConfig().Fdump(snapshot, v)
 		}
 	}