### Question:
Doubles { public static Mapper<BigInteger, Double> fromBigIntegerToDouble() { return new Mapper<BigInteger, Double>() { @Override public Double map(BigInteger input) { return input.doubleValue(); } }; }  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 returnsMapperFromBigIntegerToDouble() { assertThat(fromBigIntegerToDouble().map(new BigInteger("1234")), is(1234D)); }
@Test(expected = NullPointerException.class) public void throwsNullPointerExceptionWhenMapperFromBigIntegerToDoublePassedNull() { fromBigIntegerToDouble().map(null); }