@Test
public void nitrogen_anion() {

    assertThat(MDLValence.implicitValence(7, -1, 0), is(2));
    assertThat(MDLValence.implicitValence(7, -1, 1), is(2));
    assertThat(MDLValence.implicitValence(7, -1, 2), is(2));
    assertThat(MDLValence.implicitValence(7, -1, 3), is(3));
    assertThat(MDLValence.implicitValence(7, -1, 4), is(4));
    assertThat(MDLValence.implicitValence(7, -1, 5), is(5));
    assertThat(MDLValence.implicitValence(7, -1, 6), is(6));
}