Updated Writing ISIS Tests Using Gtest and Ctest (markdown)

# Creating a new test suite

## For a Class

1. Create a new file `ClassNameTests.cpp` in `isis/tests/`. For example, the tests for the Cube class should be in `CubeTests.cpp`.

1. Add `#include "gmock/gmock.h"` to the file.

1. Write your test cases.

1. Delete old tests

## For an Application

1. Create a new file `FunctionalTestAppname.cpp` in `isis/tests/`. For example, the tests the application `isisimport` should be in `FunctionalTestIsisImport.cpp`.

1. Add you tests to this file

1. Delete the tests and all of the test directories  

Note: If your tests require the use of ISIS's Null value, you will need to include SpecialPixel.h

# General Testing Tips