diff --git a/internal/ui/spinner_coverage_test.go b/internal/ui/spinner_coverage_test.go
new file mode 100644
index 00000000..07b2b4ea
--- /dev/null
+++ b/internal/ui/spinner_coverage_test.go
@@ -0,0 +1,73 @@
+package ui
+
+import (
+	"bytes"
+	"os"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestNewline(t *testing.T) {
+	var b bytes.Buffer
+	New(&b).Newline()
+	if b.String() != "\n" {
+		t.Errorf("Newline = %q, want a single newline", b.String())
+	}
+}
+
+func TestAutoColor(t *testing.T) {
+	orig, had := os.LookupEnv("NO_COLOR")
+	t.Cleanup(func() {
+		if had {
+			_ = os.Setenv("NO_COLOR", orig)
+		} else {
+			_ = os.Unsetenv("NO_COLOR")
+		}
+	})
+
+	// NO_COLOR set → false regardless of the writer.
+	_ = os.Setenv("NO_COLOR", "1")
+	if autoColor(os.Stdout) {
+		t.Error("NO_COLOR set → autoColor must be false")
+	}
+
+	// NO_COLOR unset from here on.
+	_ = os.Unsetenv("NO_COLOR")
+	// A non-*os.File writer (a buffer) → false.
+	if autoColor(&bytes.Buffer{}) {
+		t.Error("a non-*os.File writer → false")
+	}
+	// An *os.File that isn't a terminal (a regular temp file) → false.
+	f, err := os.CreateTemp(t.TempDir(), "ui-*")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() { _ = f.Close() }()
+	if autoColor(f) {
+		t.Error("a non-terminal *os.File → false")
+	}
+}
+
+// TestSpinner_Static: color off → the one-line static spinner + a no-op Stop.
+func TestSpinner_Static(t *testing.T) {
+	var b bytes.Buffer
+	s := New(&b).Spinner("working", "hint")
+	s.Stop() // static → no-op, idempotent
+	if !strings.Contains(b.String(), "working") {
+		t.Errorf("static spinner should print its message, got %q", b.String())
+	}
+}
+
+// TestSpinner_Animated: color on → the animated goroutine. Sleeping past one
+// 120ms tick covers run's tick arm (frame advance + redraw); Stop drains the
+// goroutine before we read, so it's race-safe under -race.
+func TestSpinner_Animated(t *testing.T) {
+	var b bytes.Buffer
+	s := New(&b, WithColor(true)).Spinner("loading", "please wait")
+	time.Sleep(150 * time.Millisecond)
+	s.Stop()
+	if !strings.Contains(b.String(), "loading") {
+		t.Errorf("animated spinner should draw its message, got %q", b.String())
+	}
+}