Cleanup: add missing headers to CMake, formatting

tests/CMakeLists.txt

@@ -30,7 +30,7 @@ endif()
 # The installation directory's Python is the best one to use. However, it can only be there after the install step,
 # which means that Python will never be there on a fresh system. To suit different needs, the user can pass
 # -DTEST_PYTHON_EXE=/path/to/python to CMake.
-if (NOT TEST_PYTHON_EXE)
+if(NOT TEST_PYTHON_EXE)
   set(TEST_PYTHON_EXE ${_default_test_python_exe})
   message(STATUS "Tests: Using Python executable: ${TEST_PYTHON_EXE}")
 elseif(NOT EXISTS ${TEST_PYTHON_EXE})