Add a TextFormatter (#50)

FollowTheProcess · web-flow · commit 2e29acf40d93 · 2025-11-16T13:11:26.000Z
# Summary
&lt;!-- Describe your changes in detail here, if it closes an open issue,
include "Closes #&lt;issue&gt;" --&gt;
diff --git a/README.md b/README.md
@@ -92,7 +92,7 @@ expression: value.Show() # The expression that generated the snapshot
 This format was inspired by [insta], a popular snapshot testing library in rust
 
 > [!TIP]
-> If you want a different format, you can implement your own! Just implement the `snapshot.Formatter` interface and pass it in
+> If you want a different format, there is also a `TextFormatter` or you can implement your own! Just implement the `snapshot.Formatter` interface and pass it in
 > with the `snapshot.WithFormatter` option and you're away!
 
 ### 🔄 Automatic Updating
diff --git a/formatter.go b/formatter.go
@@ -1,9 +1,30 @@
 package snapshot
 
+import (
+	"go.followtheprocess.codes/snapshot/internal/format/insta"
+	"go.followtheprocess.codes/snapshot/internal/format/text"
+)
+
 // Formatter is an interface describing something capable of producing a snapshot.
 type Formatter interface {
 	// Format returns a formatted version of 'value' as a raw byte slice, these
 	// bytes are interpreted as the snapshot and will be written and read from disk
 	// during snapshot comparisons.
 	Format(value any) ([]byte, error)
 }
+
+// InstaFormatter returns a [Formatter] that produces snapshots in the [insta]
+// yaml format.
+//
+// It takes a description for the snapshot.
+//
+// [insta]: https://crates.io/crates/insta
+func InstaFormatter(description string) Formatter {
+	return insta.NewFormatter(description)
+}
+
+// TextFormatter returns a [Formatter] that produces snapshots by simply
+// dumping the value as plain text.
+func TextFormatter() Formatter {
+	return text.NewFormatter()
+}
diff --git a/internal/format/insta/insta.go b/internal/format/insta/insta.go
@@ -63,7 +63,7 @@ func (s Snapshot) save(w io.Writer) error {
 	return nil
 }
 
-// Formatter implements the [format.Formatter] interface and returns an
+// Formatter implements the [snapshot.Formatter] interface and returns an
 // insta-compatible snapshot format.
 type Formatter struct {
 	description string
diff --git a/internal/format/insta/insta_test.go b/internal/format/insta/insta_test.go
@@ -37,7 +37,7 @@ func TestFormatter(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			path := filepath.Join("testdata", "TestSave", tt.name+".snap")
+			path := filepath.Join("testdata", "TestFormatter", tt.name+".snap")
 
 			want, err := os.ReadFile(path)
 			test.Ok(t, err)
diff --git a/internal/format/insta/testdata/TestFormatter/empty.snap b/internal/format/insta/testdata/TestFormatter/empty.snap
diff --git a/internal/format/insta/testdata/TestFormatter/ints.snap b/internal/format/insta/testdata/TestFormatter/ints.snap
diff --git a/internal/format/insta/testdata/TestFormatter/string.snap b/internal/format/insta/testdata/TestFormatter/string.snap
diff --git a/internal/format/insta/testdata/TestFormatter/struct.snap b/internal/format/insta/testdata/TestFormatter/struct.snap
diff --git a/internal/format/text/testdata/TestFormatter/empty.snap b/internal/format/text/testdata/TestFormatter/empty.snap
@@ -0,0 +1 @@
+<nil>
diff --git a/internal/format/text/testdata/TestFormatter/int.snap b/internal/format/text/testdata/TestFormatter/int.snap
@@ -0,0 +1 @@
+42
diff --git a/internal/format/text/testdata/TestFormatter/slice.snap b/internal/format/text/testdata/TestFormatter/slice.snap
@@ -0,0 +1 @@
+[]string{"one", "two", "three"}
diff --git a/internal/format/text/testdata/TestFormatter/stringer.snap b/internal/format/text/testdata/TestFormatter/stringer.snap
@@ -0,0 +1 @@
+stringer
diff --git a/internal/format/text/testdata/TestFormatter/struct.snap b/internal/format/text/testdata/TestFormatter/struct.snap
@@ -0,0 +1 @@
+text_test.person{name:"Tom", age:31}
diff --git a/internal/format/text/testdata/TestFormatter/text_marshaler.snap b/internal/format/text/testdata/TestFormatter/text_marshaler.snap
@@ -0,0 +1 @@
+hello
diff --git a/internal/format/text/text.go b/internal/format/text/text.go
@@ -0,0 +1,42 @@
+// Package text provides a simple text formatter for snapshots.
+package text
+
+import (
+	"bytes"
+	"encoding"
+	"fmt"
+)
+
+// Formatter implements [snapshot.Formatter] and returns a simple plain text
+// snapshot format.
+type Formatter struct{}
+
+// NewFormatter returns a new Formatter.
+func NewFormatter() Formatter {
+	return Formatter{}
+}
+
+// Format returns a plain text snapshot of the value.
+func (f Formatter) Format(value any) ([]byte, error) {
+	buf := &bytes.Buffer{}
+
+	switch val := value.(type) {
+	case encoding.TextMarshaler:
+		content, err := val.MarshalText()
+		if err != nil {
+			return nil, err
+		}
+
+		buf.Write(content)
+	case fmt.Stringer:
+		buf.WriteString(val.String())
+	case string, []byte, int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, uintptr, bool, float32, float64, complex64, complex128:
+		// For any primitive type just use %+v
+		fmt.Fprintf(buf, "%+v", val)
+	default:
+		// Fallback, use %#v as a best effort at generic printing
+		fmt.Fprintf(buf, "%#v", val)
+	}
+
+	return buf.Bytes(), nil
+}
diff --git a/internal/format/text/text_test.go b/internal/format/text/text_test.go
@@ -0,0 +1,79 @@
+package text_test
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"go.followtheprocess.codes/snapshot/internal/format/text"
+	"go.followtheprocess.codes/test"
+)
+
+type textMarshaler struct {
+	txt string
+}
+
+func (t textMarshaler) MarshalText() ([]byte, error) {
+	return []byte(t.txt), nil
+}
+
+type stringer struct {
+	txt string
+}
+
+func (s stringer) String() string {
+	return s.txt
+}
+
+type person struct {
+	name string
+	age  int
+}
+
+func TestFormatter(t *testing.T) {
+	tests := []struct {
+		value any
+		name  string
+	}{
+		{
+			name:  "empty",
+			value: nil,
+		},
+		{
+			name:  "text_marshaler",
+			value: textMarshaler{txt: "hello"},
+		},
+		{
+			name:  "stringer",
+			value: stringer{txt: "stringer"},
+		},
+		{
+			name:  "int",
+			value: 42,
+		},
+		{
+			name:  "slice",
+			value: []string{"one", "two", "three"},
+		},
+		{
+			name:  "struct",
+			value: person{name: "Tom", age: 31},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			test.ColorEnabled(os.Getenv("CI") == "")
+
+			path := filepath.Join("testdata", "TestFormatter", tt.name+".snap")
+
+			want, err := os.ReadFile(path)
+			test.Ok(t, err)
+
+			got, err := text.NewFormatter().Format(tt.value)
+			test.Ok(t, err)
+
+			test.DiffBytes(t, got, want)
+		})
+	}
+}
diff --git a/snapshot.go b/snapshot.go
@@ -14,7 +14,6 @@ import (
 
 	"go.followtheprocess.codes/hue"
 	"go.followtheprocess.codes/snapshot/internal/diff"
-	"go.followtheprocess.codes/snapshot/internal/format/insta"
 )
 
 const (
@@ -110,7 +109,7 @@ func (r Runner) Snap(value any) {
 		//
 		//nolint:revive // Suspicious value receiver modified but actually this is fine
 		// as all we care about is this one function call
-		r.formatter = insta.NewFormatter(r.description)
+		r.formatter = InstaFormatter(r.description)
 	}
 
 	content, err := r.formatter.Format(value)

Original file line number	Diff line number	Diff line change
`@@ -63,7 +63,7 @@ func (s Snapshot) save(w io.Writer) error {`
`63`	`63`	`return nil`
`64`	`64`	`}`
`65`	`65`
`66`		`-// Formatter implements the [format.Formatter] interface and returns an`
	`66`	`+// Formatter implements the [snapshot.Formatter] interface and returns an`
`67`	`67`	`// insta-compatible snapshot format.`
`68`	`68`	`type Formatter struct {`
`69`	`69`	`description string`