@Test
public void testAngleAxis() {

  final Matrix3 mat3A = new Matrix3();
  // rotate identity 90 degrees around X
  final double angle = MathUtils.HALF_PI;
  mat3A.fromAngleAxis(MathUtils.HALF_PI, Vector3.UNIT_X);
  assertEquals(new Matrix3( //
      1, 0, 0, //
      0, Math.cos(angle), -Math.sin(angle), //
      0, Math.sin(angle), Math.cos(angle)), mat3A);
}