### Question:
BigIntegers { public static Mapper<Double, BigInteger> fromDoubleToBigInteger() { return new Mapper<Double, BigInteger>() { @Override public BigInteger map(Double input) { return new BigInteger(((Long) input.longValue()).toString()); } }; }  static Mapper<String, BigInteger> fromStringToBigInteger(); static Mapper<Integer, BigInteger> fromIntegerToBigInteger(); static Mapper<Long, BigInteger> fromLongToBigInteger(); static Mapper<Float, BigInteger> fromFloatToBigInteger(); static Mapper<Double, BigInteger> fromDoubleToBigInteger(); static Mapper<BigDecimal, BigInteger> fromBigDecimalToBigInteger();  }### Answer:
@Test public void returnsMapperFromDoubleToBigInteger() { assertThat(fromDoubleToBigInteger().map(1234.56D), is(new BigInteger("1234"))); }
@Test(expected = NullPointerException.class) public void throwsNullPointerExceptionWhenMapperFromDoubleToBigIntegerPassedNull() { fromDoubleToBigInteger().map(null); }