Test getValue() for unit FAHRENHEIT

getValueTestForFAHRENHEITequal0(): Test getValue() for unit FAHRENHEIT
with temperature value 0. This value is chosen since the FAHRENHEIT
value is converted twice based on the relationship with kelvin, where
the result of division may not be indentical. In this test case,  the
test result is a failure.
getValueTestForFAHRENHEITequal0KELVIN(): Test getValue() for unit
FAHRENHEIT with temperature value -459.67. This value is chosen to
cancel out the value while converting to kelvin, and use 0 to convert
back to FAHRENHEIT.