### Question:
Integers { public static Mapper<String, Integer> fromStringToInteger() { return new Mapper<String, Integer>() { @Override public Integer map(String input) { checkNotNull(input); return Integer.valueOf(input); } }; }  static Mapper<String, Integer> fromStringToInteger(); static Mapper<Long, Integer> fromLongToInteger(); static Mapper<BigInteger, Integer> fromBigIntegerToInteger(); static Mapper<Float, Integer> fromFloatToInteger(); static Mapper<Double, Integer> fromDoubleToInteger(); static Mapper<BigDecimal, Integer> fromBigDecimalToInteger();  }### Answer:
@Test public void returnsMapperFromStringToInteger() { assertThat(fromStringToInteger().map("1234"), is(1234)); }
@Test(expected = NullPointerException.class) public void throwsNullPointerExceptionWhenMapperFromStringToIntegerPassedNull() { fromStringToInteger().map(null); }