diff --git a/internal/affine/colorm_test.go b/internal/affine/colorm_test.go
new file mode 100644
index 000000000..ff2c64a2c
--- /dev/null
+++ b/internal/affine/colorm_test.go
@@ -0,0 +1,81 @@
+// Copyright 2019 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package affine_test
+
+import (
+	"math"
+	"testing"
+
+	. "github.com/hajimehoshi/ebiten/internal/affine"
+)
+
+func TestColorMScaleOnly(t *testing.T) {
+	cases := []struct {
+		In  *ColorM
+		Out bool
+	}{
+		{
+			nil,
+			true,
+		},
+		{
+			(*ColorM)(nil).Translate(0, 0, 0, 0),
+			true,
+		},
+		{
+			(*ColorM)(nil).Translate(1, 0, 0, 0),
+			false,
+		},
+		{
+			(*ColorM)(nil).Translate(0, 0, 0, -1),
+			false,
+		},
+		{
+			(*ColorM)(nil).Scale(1, 1, 1, 1),
+			true,
+		},
+		{
+			(*ColorM)(nil).Scale(0, 0, 0, 0),
+			true,
+		},
+		{
+			(*ColorM)(nil).Scale(0.1, 0.2, 0.3, 0.4),
+			true,
+		},
+		{
+			(*ColorM)(nil).Scale(0.1, 0.2, 0.3, 0.4).Translate(1, 0, 0, 0),
+			false,
+		},
+		{
+			(*ColorM)(nil).ChangeHSV(math.Pi/2, 0.5, 0.5),
+			false,
+		},
+		{
+			(*ColorM)(nil).SetElement(0, 0, 2),
+			true,
+		},
+		{
+			(*ColorM)(nil).SetElement(0, 1, 2),
+			false,
+		},
+	}
+	for _, c := range cases {
+		got := c.In.ScaleOnly()
+		want := c.Out
+		if got != want {
+			t.Errorf("%v.ScaleOnly(): got: %t, want: %t", c.In, got, want)
+		}
+	}
+}