Find method to clarify gtest output statements.

[SanTransisco]

Generally, we can perform the tests then the test will give an output on how the test failed. But, this isn't immediately clear to the students sometimes. We have been getting by doing

ASSERT_EQ(output, expected) <<outputMessage;

but we should see if we can find a way to better communicate to the students where, and how they went wrong.
Here is the code I've been using so far for analyzing standard output, but its gonna need some work for sure.

#define ASSERT_STD_OUTPUT_MSG(expected,outputmessage, func) { \
  std::stringstream ss; \
  auto old_buf = std::cout.rdbuf(ss.rdbuf()); \
  func(); \
  std::cout.rdbuf(old_buf); \
  std::string output = ss.str(); \
  ASSERT_EQ(output, expected) << outputmessage; \
}

[pinventado]

We probably want to refactor the code that is currently used to fit into the pattern of EXPECT_PRED_FORMAT*. I've started doing this here:

https://github.com/ILXL/cpp-code-analyzer/blob/7b2b1957678d6a7369eb7e73f7d43b7346473aea/src/test/gtest_ext.h#L196

but need to reflect it in the other macros. Using this pattern should allow us to attach additional output messages.