Fix iwyu integration test by creating compile_commands.json

The iwyu integration test was passing when it should fail because
include-what-you-use needs a compilation database (compile_commands.json)
to properly analyze files.

The integration_test function was not creating compile_commands.json
before running pre-commit, so iwyu couldn't detect unused includes.

Added call to set_compilation_db() to create the compilation database
for integration tests, matching the shell command test setup.

Author: pocc

tests/test_utils.py

@@ -113,6 +113,8 @@ def integration_test(cmd_name, files, args, test_dir):
         if test_file_base in test_file_strs:
             with open(test_file, "w") as fd:
                 fd.write(test_file_strs[test_file_base])
+    # Create compilation database for clang-tidy and iwyu
+    set_compilation_db(files)
     # Add only the files we are testing
     run_in(["git", "reset"], test_dir)
     run_in(["git", "add"] + files, test_dir)