assertThrows(IllegalArgumentException.class, () -> LinearTransformation.horizontal(Double.NaN));
  }

  public void testForNaN() {
    LinearTransformation transformation = LinearTransformation.forNaN();
    assertLinearTransformationNaN(transformation);
  }

    assertThrows(IllegalArgumentException.class, () -> LinearTransformation.horizontal(Double.NaN));
  }

  public void testForNaN() {
    LinearTransformation transformation = LinearTransformation.forNaN();
    assertLinearTransformationNaN(transformation);
  }

    assertThat(transformation.inverse().inverse()).isSameInstanceAs(transformation);
  }

  /**
   * Asserts that {@code transformation} behaves as expected for {@link
   * LinearTransformation#forNaN}.
   */
  static void assertLinearTransformationNaN(LinearTransformation transformation) {
    assertThat(transformation.isHorizontal()).isFalse();
    assertThat(transformation.isVertical()).isFalse();

    assertThat(transformation.inverse().inverse()).isSameInstanceAs(transformation);
  }

  /**
   * Asserts that {@code transformation} behaves as expected for {@link
   * LinearTransformation#forNaN}.
   */
  static void assertLinearTransformationNaN(LinearTransformation transformation) {
    assertThat(transformation.isHorizontal()).isFalse();
    assertThat(transformation.isVertical()).isFalse();