public void clear() {
    mUserProps.clear();
    mSources.clear();
  }
@Test
  public void clear() {
    mProperties.put(mKeyWithValue, "ignored1", Source.RUNTIME);
    mProperties.put(mKeyWithoutValue, "ignored2", Source.RUNTIME);
    mProperties.clear();
    assertEquals(null, mProperties.get(mKeyWithoutValue));
    assertEquals("value", mProperties.get(mKeyWithValue));
  }