Update tests to latest version of gtest

[brtietz]

In https://github.com/NREL/ssc/runs/6181437239?check_suite_focus=true, the tests failed due to an incompatibility with the latest version of gtest with the following error:

In file included from /Users/runner/work/ssc/ssc/ssc/test/ssc_test/cmod_tcstrough_empirical_test.cpp:23:
In file included from /Users/runner/work/ssc/ssc/googletest/googletest/include/gtest/gtest.h:60:
In file included from /Users/runner/work/ssc/ssc/googletest/googletest/include/gtest/gtest-death-test.h:43:
In file included from /Users/runner/work/ssc/ssc/googletest/googletest/include/gtest/internal/gtest-death-test-internal.h:46:
In file included from /Users/runner/work/ssc/ssc/googletest/googletest/include/gtest/gtest-matchers.h:48:
In file included from /Users/runner/work/ssc/ssc/googletest/googletest/include/gtest/gtest-printers.h:114:
/Users/runner/work/ssc/ssc/googletest/googletest/include/gtest/internal/gtest-internal.h:477:40: error: cannot initialize return object of type 'testing::Test *' with an rvalue of type 'csp_trough_EmpiricalTroughCmod_Phoenix_NoFinancial_Test '
Test CreateTest() override { return new TestClass; }
^~~
/Users/runner/work/ssc/ssc/ssc/test/ssc_test/cmod_tcstrough_empirical_test.cpp:233:1: note: in instantiation of member function 'testing::internal::TestFactoryImpl<csp_trough_EmpiricalTroughCmod_Phoenix_NoFinancial_Test>::CreateTest' requested here
NAMESPACE_TEST(csp_trough, EmpiricalTroughCmod, Phoenix_NoFinancial)
^
/Users/runner/work/ssc/ssc/ssc/test/shared_test/vs_google_test_explorer_namespace.h:45:3: note: expanded from macro 'NAMESPACE_TEST'
NAMESPACE_GTEST_TEST_(namespace_name, test_case_name, test_name,
^
/Users/runner/work/ssc/ssc/ssc/test/shared_test/vs_google_test_explorer_namespace.h:38:13: note: expanded from macro 'NAMESPACE_GTEST_TEST_'
new ::testing::internal::TestFactoryImpl<
^
16 errors generated.

The short term fix was to pin the version of gtest at the last version that worked: #804

This issue covers the long term fix: rewriting our tests to remove the errors.

[dguittet]

This is resolved in #1035

[tyneises]

@dguittet can we update Step 4 in the build instructions? https://github.com/NREL/SAM/wiki/Windows-Build-Instructions

[brtietz]

That's tricky - 1035 is going to go into develop for the 2024 release, but the issue will still exist on patch (current develop). Is there a way to cherry-pick the fix to the current branch?

[dguittet]

I think it'll be possible to isolate the fix for patch

[dguittet]

@tyneises I don't think we can change the googletest version until this has been merged though