add blacher fixture #346

Job	Run time
build-and-test (Windows-MSVC, windows-latest, cl, cl)	2s
build-and-test (macOS-Clang, macos-latest, clang, clang++)	4s
build-and-test (Ubuntu-Clang, ubuntu-latest, clang, clang++)	4s
build-and-test (Ubuntu-GCC, ubuntu-latest, gcc, g++)	3s
Publish Tests Results	2s
	15s

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