### Question:
Doubles { public static Mapper<String, Double> fromStringToDouble() { return new Mapper<String, Double>() { @Override public Double map(String input) { return Double.valueOf(input); } }; }  static Mapper<String, Double> fromStringToDouble(); static Mapper<Integer, Double> fromIntegerToDouble(); static Mapper<Long, Double> fromLongToDouble(); static Mapper<BigInteger, Double> fromBigIntegerToDouble(); static Mapper<Float, Double> fromFloatToDouble(); static Mapper<BigDecimal, Double> fromBigDecimalToDouble();  }### Answer:
@Test public void returnsMapperFromStringToDouble() { assertThat(fromStringToDouble().map("12345678"), is(12345678D)); }
@Test(expected = NullPointerException.class) public void throwsNullPointerExceptionWhenMapperFromStringToDoublePassedNull() { fromStringToDouble().map(null); }