Add an option which disables unit tests and gtest (#238)

Defaults to off, but allows the user to disable unit test
targets. This is particularly useful for target which are not
supported by gtest.

CMakeLists.txt

@@ -27,14 +27,15 @@ project (icubaby
   DESCRIPTION "Little Library to Immediately Convert Unicode"
   LANGUAGES C CXX
 )
-option (ICUBABY_COVERAGE "Generate LLVM Source-based Coverage")
-option (ICUBABY_CXX17 "Use C++17 (rather than the default C++20)")
-option (ICUBABY_EXAMPLES "Include example code in the generated build")
-option (ICUBABY_FUZZTEST "Enable FuzzTest")
+option (ICUBABY_COVERAGE "Generate LLVM Source-based Coverage" No)
+option (ICUBABY_CXX17 "Use C++17 (rather than the default C++20)" No)
+option (ICUBABY_EXAMPLES "Include example code in the generated build" No)
+option (ICUBABY_FUZZTEST "Enable FuzzTest (if yes, overrides ICUBABY_UNIT_TESTS)" No)
 option (ICUBABY_LIBCXX "Use libc++ rather than libstdc++ (clang only)")
-option (ICUBABY_SANITIZE "Enable undefined behavior- and address-sanitizers where supported")
-option (ICUBABY_STANDALONE "A standalone build includes test executables")
-option (ICUBABY_WERROR "Compiler warnings are errors")
+option (ICUBABY_SANITIZE "Enable undefined behavior- and address-sanitizers where supported" No)
+option (ICUBABY_STANDALONE "A standalone build includes test executables" No)
+option (ICUBABY_UNIT_TESTS "Include unit tests (and the Google Test framework) in the generated build?" Yes)
+option (ICUBABY_WERROR "Compiler warnings are errors" No)
 
 set (icubaby_project_root "${CMAKE_CURRENT_SOURCE_DIR}")
 list (APPEND CMAKE_MODULE_PATH "${icubaby_project_root}/cmake")
@@ -56,7 +57,9 @@ if (ICUBABY_FUZZTEST)
   include (GoogleTest)
   fuzztest_setup_fuzzing_flags ()
 else ()
-  setup_gtest ()
+  if (ICUBABY_UNIT_TESTS)
+    setup_gtest ()
+  endif (ICUBABY_UNIT_TESTS)
 endif (ICUBABY_FUZZTEST)
 enable_testing ()
 
@@ -104,7 +107,7 @@ if (ICUBABY_STANDALONE)
     add_subdirectory (tests)
 endif (ICUBABY_STANDALONE)
 
-if (TARGET gtest)
+if (ICUBABY_UNIT_TESTS AND TARGET gtest)
   add_subdirectory (unittests)
 endif ()