@Test
public void nitrogen_cation() {

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