### Question:
BigIntegers { public static Mapper<Integer, BigInteger> fromIntegerToBigInteger() { return new Mapper<Integer, BigInteger>() { @Override public BigInteger map(Integer input) { return new BigInteger(input.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 returnsMapperFromIntegerToBigInteger() { assertThat(fromIntegerToBigInteger().map(1234), is(new BigInteger("1234"))); }
@Test(expected = NullPointerException.class) public void throwsNullPointerExceptionWhenMapperFromIntegerToBigIntegerPassedNull() { fromIntegerToBigInteger().map(null); }