test(printer): isolate color environment and verify opt-out

printer/html_test.go

@@ -67,6 +67,7 @@ func TestPrettyHTMLVoidTagsAndComments(t *testing.T) {
 }
 
 func TestPrettyHTMLColorization(t *testing.T) {
+	t.Setenv("NO_COLOR", "")
 	input := `<div class="container">Content</div>`
 	var buf bytes.Buffer
 	_, err := PrettyHTML(&buf, strings.NewReader(input), true) // enabled = true

printer/json_test.go

@@ -31,6 +31,7 @@ func TestPrettyJSON(t *testing.T) {
 }
 
 func TestPrettyJSONColored(t *testing.T) {
+	t.Setenv("NO_COLOR", "")
 	input := `{"key": "value", "num": 42}`
 	var buf bytes.Buffer
 	_, err := PrettyJSON(&buf, strings.NewReader(input), true)

printer/no_color_test.go

@@ -0,0 +1,32 @@
+package printer
+
+import (
+	"bytes"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestPrettyRespectsNoColorEnvironment(t *testing.T) {
+	t.Setenv("NO_COLOR", "1")
+	for _, tc := range []struct {
+		name, input string
+		format      func(io.Writer, io.Reader, bool) (int64, error)
+	}{
+		{"json", `{"value":42}`, PrettyJSON},
+		{"html", `<div class="content">Hello</div>`, PrettyHTML},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			var out bytes.Buffer
+			if _, err := tc.format(&out, strings.NewReader(tc.input), true); err != nil {
+				t.Fatal(err)
+			}
+			if out.Len() == 0 {
+				t.Fatal("empty output")
+			}
+			if strings.Contains(out.String(), "\x1b[") {
+				t.Fatalf("NO_COLOR output contains ANSI codes: %q", out.String())
+			}
+		})
+	}
+}