@Override
  public boolean isDetected() {
    return "true".equalsIgnoreCase(system.envVariable("TF_BUILD"));
  }
@Test
  public void isDetected() {
    setEnvVariable("TF_BUILD", "True");
    assertThat(underTest.isDetected()).isTrue();

    setEnvVariable("TF_BUILD", "true");
    assertThat(underTest.isDetected()).isTrue();

    setEnvVariable("CI", "true");
    setEnvVariable("APPVEYOR", null);
    setEnvVariable("TF_BUILD", null);
    assertThat(underTest.isDetected()).isFalse();
  }