diff --git a/libraries/transformer/src/test/java/androidx/media3/transformer/ChannelMixingMatrixTest.java b/libraries/transformer/src/test/java/androidx/media3/transformer/ChannelMixingMatrixTest.java
new file mode 100644
index 0000000000..162e0a4f01
--- /dev/null
+++ b/libraries/transformer/src/test/java/androidx/media3/transformer/ChannelMixingMatrixTest.java
@@ -0,0 +1,145 @@
+/*
+ * Copyright 2023 The Android Open Source Project
+ *
+ * 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 androidx.media3.transformer;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+/** Unit tests for {@link ChannelMixingMatrix}. */
+@RunWith(AndroidJUnit4.class)
+public class ChannelMixingMatrixTest {
+
+  @Test
+  public void allZeroValues_3To2_hasCorrectProperties() {
+    int inputCount = 3;
+    int outputCount = 2;
+    float[] coefficients =
+        new float[] {
+          0f, 0f,
+          0f, 0f,
+          0f, 0f,
+        };
+
+    ChannelMixingMatrix matrix = new ChannelMixingMatrix(inputCount, outputCount, coefficients);
+    assertThat(matrix.isZero()).isTrue();
+    assertThat(matrix.isSquare()).isFalse();
+    assertThat(matrix.isDiagonal()).isFalse();
+  }
+
+  @Test
+  public void allZeroValues_3To3_hasCorrectProperties() {
+    int inputCount = 3;
+    int outputCount = 3;
+    float[] coefficients =
+        new float[] {
+          0f, 0f, 0f,
+          0f, 0f, 0f,
+          0f, 0f, 0f,
+        };
+
+    ChannelMixingMatrix matrix = new ChannelMixingMatrix(inputCount, outputCount, coefficients);
+    assertThat(matrix.isZero()).isTrue();
+    assertThat(matrix.isSquare()).isTrue();
+    assertThat(matrix.isDiagonal()).isTrue();
+  }
+
+  @Test
+  public void allZeroValues_3To4_hasCorrectProperties() {
+    int inputCount = 3;
+    int outputCount = 4;
+    float[] coefficients =
+        new float[] {
+          0f, 0f, 0f, 0f,
+          0f, 0f, 0f, 0f,
+          0f, 0f, 0f, 0f,
+        };
+
+    ChannelMixingMatrix matrix = new ChannelMixingMatrix(inputCount, outputCount, coefficients);
+    assertThat(matrix.isZero()).isTrue();
+    assertThat(matrix.isSquare()).isFalse();
+    assertThat(matrix.isDiagonal()).isFalse();
+  }
+
+  @Test
+  public void oneNonZeroValue_3To4_hasCorrectProperties() {
+    int inputCount = 3;
+    int outputCount = 4;
+    float[] coefficients =
+        new float[] {
+          0f, 0f, 0f, 0f,
+          0f, 0f, 0f, 0.2f,
+          0f, 0f, 0f, 0f,
+        };
+
+    ChannelMixingMatrix matrix = new ChannelMixingMatrix(inputCount, outputCount, coefficients);
+    assertThat(matrix.isZero()).isFalse();
+    assertThat(matrix.isSquare()).isFalse();
+    assertThat(matrix.isDiagonal()).isFalse();
+  }
+
+  @Test
+  public void zeroValuesOnDiagonal_2To2_hasCorrectProperties() {
+    int inputCount = 2;
+    int outputCount = 2;
+    float[] coefficients =
+        new float[] {
+          0f, 1f,
+          2f, 0f,
+        };
+
+    ChannelMixingMatrix matrix = new ChannelMixingMatrix(inputCount, outputCount, coefficients);
+    assertThat(matrix.isZero()).isFalse();
+    assertThat(matrix.isSquare()).isTrue();
+    assertThat(matrix.isDiagonal()).isFalse();
+  }
+
+  @Test
+  public void nonZeroValuesOnDiagonal_4To4_hasCorrectProperties() {
+    int inputCount = 4;
+    int outputCount = 4;
+    float[] coefficients =
+        new float[] {
+          1f, 0f, 0f, 0f,
+          0f, 2f, 0f, 0f,
+          0f, 0f, 3f, 0f,
+          0f, 0f, 0f, 0f,
+        };
+
+    ChannelMixingMatrix matrix = new ChannelMixingMatrix(inputCount, outputCount, coefficients);
+    assertThat(matrix.isZero()).isFalse();
+    assertThat(matrix.isSquare()).isTrue();
+    assertThat(matrix.isDiagonal()).isTrue();
+  }
+
+  @Test
+  public void allNonZeroValues_2To4_hasCorrectProperties() {
+    int inputCount = 2;
+    int outputCount = 4;
+    float[] coefficients =
+        new float[] {
+          1f, 3f, 5f, 10f,
+          4f, 2f, 9f, 123f,
+        };
+
+    ChannelMixingMatrix matrix = new ChannelMixingMatrix(inputCount, outputCount, coefficients);
+    assertThat(matrix.isZero()).isFalse();
+    assertThat(matrix.isSquare()).isFalse();
+    assertThat(matrix.isDiagonal()).isFalse();
+  }
+}