Use error structs instead of fmt.Errorf (#55)

* Refactor errors

* Fix go vet

cupaloy.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"os"
 	"strings"
+
+	"github.com/bradleyjkemp/cupaloy/v2/internal"
 )
 
 // New constructs a new, configured instance of cupaloy using the given
@@ -101,9 +103,9 @@ func (c *Config) snapshot(snapshotName string, i ...interface{}) error {
 	prevSnapshot, err := c.readSnapshot(snapshotName)
 	if os.IsNotExist(err) {
 		if c.createNewAutomatically {
-			return c.updateSnapshot(snapshotName, snapshot)
+			return c.updateSnapshot(snapshotName, prevSnapshot, snapshot)
 		}
-		return fmt.Errorf("snapshot does not exist for test %s", snapshotName)
+		return internal.ErrNoSnapshot{Name: snapshotName}
 	}
 	if err != nil {
 		return err
@@ -116,9 +118,10 @@ func (c *Config) snapshot(snapshotName string, i ...interface{}) error {
 
 	if c.shouldUpdate() {
 		// updates snapshot to current value and upgrades snapshot format
-		return c.updateSnapshot(snapshotName, snapshot)
+		return c.updateSnapshot(snapshotName, prevSnapshot, snapshot)
 	}
 
-	diff := diffSnapshots(prevSnapshot, snapshot)
-	return fmt.Errorf("snapshot not equal:\n%s", diff)
+	return internal.ErrSnapshotMismatch{
+		Diff: diffSnapshots(prevSnapshot, snapshot),
+	}
 }

examples/advanced_test.go

@@ -2,6 +2,7 @@ package examples_test
 
 import (
 	"bytes"
+	"github.com/bradleyjkemp/cupaloy/v2/internal"
 	"io/ioutil"
 	"strings"
 	"testing"
@@ -49,6 +50,7 @@ func TestConfig(t *testing.T) {
 // This is to prevent you accidentally updating your snapshots in CI
 func TestUpdate(t *testing.T) {
 	snapshotter := cupaloy.New(cupaloy.EnvVariableName("HOME"))
+	defer snapshotter.Snapshot("Hello world") // reset snapshot to known state
 
 	err := snapshotter.Snapshot("Hello world")
 	if err != nil {
@@ -59,11 +61,11 @@ func TestUpdate(t *testing.T) {
 	if err == nil {
 		t.Fatalf("Updating a snapshot with a new value is always an error %s", err)
 	}
-	if err.Error() != "snapshot updated for test examples_test-TestUpdate" {
-		t.Fatalf("Error returned will say that snapshot was updated")
+	if _, ok := err.(internal.ErrSnapshotUpdated); !ok {
+		t.Fatalf("Error returned will be of type ErrSnapshotUpdated")
 	}
 
-	snapshotter.Snapshot("Hello world") // reset snapshot to known state
+
 }
 
 // If a snapshot doesn't exist then it is created and an error returned
@@ -81,8 +83,8 @@ func TestMissingSnapshot(t *testing.T) {
 	if err == nil {
 		t.Fatalf("This will always return an error %s", err)
 	}
-	if err.Error() != "snapshot created for test examples_test-TestMissingSnapshot" {
-		t.Fatalf("Error returned will say that snapshot was created %s", err)
+	if _, ok := err.(internal.ErrSnapshotCreated); !ok {
+		t.Fatalf("Error returned will be of type ErrSnapshotCreated")
 	}
 }
 

internal/errors.go

@@ -0,0 +1,37 @@
+package internal
+
+import "fmt"
+
+type ErrSnapshotCreated struct {
+	Name     string
+	Contents string
+}
+
+func (e ErrSnapshotCreated) Error() string {
+	return fmt.Sprintf("snapshot created for test %s, with contents:\n%s", e.Name, e.Contents)
+}
+
+type ErrSnapshotUpdated struct {
+	Name string
+	Diff string
+}
+
+func (e ErrSnapshotUpdated) Error() string {
+	return fmt.Sprintf("snapshot %s updated:\n%s", e.Name, e.Diff)
+}
+
+type ErrSnapshotMismatch struct {
+	Diff string
+}
+
+func (e ErrSnapshotMismatch) Error() string {
+	return fmt.Sprintf("snapshot not equal:\n%s", e.Diff)
+}
+
+type ErrNoSnapshot struct {
+	Name string
+}
+
+func (e ErrNoSnapshot) Error() string {
+	return fmt.Sprintf("snapshot %s does not exist", e.Name)
+}

util.go

@@ -3,13 +3,14 @@ package cupaloy
 import (
 	"bytes"
 	"errors"
-	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
 	"strings"
 
+	"github.com/bradleyjkemp/cupaloy/v2/internal"
+
 	"github.com/davecgh/go-spew/spew"
 	"github.com/pmezard/go-difflib/difflib"
 )
@@ -89,7 +90,7 @@ func (c *Config) readSnapshot(snapshotName string) (string, error) {
 	return string(buf), nil
 }
 
-func (c *Config) updateSnapshot(snapshotName string, snapshot string) error {
+func (c *Config) updateSnapshot(snapshotName string, prevSnapshot string, snapshot string) error {
 	// check that subdirectory exists before writing snapshot
 	err := os.MkdirAll(c.subDirName, os.ModePerm)
 	if err != nil {
@@ -110,11 +111,19 @@ func (c *Config) updateSnapshot(snapshotName string, snapshot string) error {
 		return nil
 	}
 
+	snapshotDiff := diffSnapshots(prevSnapshot, snapshot)
+
 	if isNewSnapshot {
-		return fmt.Errorf("snapshot created for test %s", snapshotName)
+		return internal.ErrSnapshotCreated{
+			Name:     snapshotName,
+			Contents: snapshot,
+		}
 	}
 
-	return fmt.Errorf("snapshot updated for test %s", snapshotName)
+	return internal.ErrSnapshotUpdated{
+		Name: snapshotName,
+		Diff: snapshotDiff,
+	}
 }
 
 func diffSnapshots(previous, current string) string {