[libc] integration test outputs header in build (#98385)

- python's unittest does not allow for custom args so sys.argv was used

Author: aaryanshukla

libc/newhdrgen/CMakeLists.txt

@@ -1,16 +1,16 @@
 if(LLVM_LIBC_FULL_BUILD)
-
   enable_testing()
 
   set(NEWHDGEN_TESTS_DIR ${CMAKE_CURRENT_SOURCE_DIR}/tests)
+  set(TEST_OUTPUT_DIR ${CMAKE_BINARY_DIR}/newhdrgen/output)
 
   add_test(
     NAME newhdrgen_integration_test
-    COMMAND ${CMAKE_COMMAND} -E env PYTHONPATH=${CMAKE_CURRENT_SOURCE_DIR} python3 ${NEWHDGEN_TESTS_DIR}/test_integration.py
+    COMMAND python3 ${NEWHDGEN_TESTS_DIR}/test_integration.py --output_dir ${TEST_OUTPUT_DIR}
   )
 
   add_custom_target(check-newhdrgen
-    COMMAND ${CMAKE_CTEST_COMMAND} -R newhdrgen_integration_test
+    COMMAND ${CMAKE_CTEST_COMMAND} -R newhdrgen_integration_test --output-on-failure
   )
 
   message(STATUS "Integration test for newhdrgen added.")

libc/newhdrgen/tests/output/test_small.h

@@ -3,23 +3,14 @@
 from pathlib import Path
 import os
 import argparse
+import sys
 
 
 class TestHeaderGenIntegration(unittest.TestCase):
     def setUp(self):
-        parser = argparse.ArgumentParser(
-            description="TestHeaderGenIntegration arguments"
-        )
-        parser.add_argument(
-            "--output_dir", type=str, help="Output directory for generated headers"
-        )
-        args, _ = parser.parse_known_args()
-        output_dir_env = os.getenv("TEST_OUTPUT_DIR")
 
         self.output_dir = Path(
-            args.output_dir
-            if args.output_dir
-            else output_dir_env if output_dir_env else "libc/newhdrgen/tests/output"
+            args.output_dir if args.output_dir else "libc/newhdrgen/tests/output"
         )
 
         self.maxDiff = None
@@ -71,4 +62,14 @@ def test_generate_header(self):
 
 
 if __name__ == "__main__":
+    parser = argparse.ArgumentParser(description="TestHeaderGenIntegration arguments")
+    parser.add_argument(
+        "--output_dir", type=str, help="Output directory for generated headers"
+    )
+    args, remaining_argv = parser.parse_known_args()
+
+    TestHeaderGenIntegration.output_dir = args.output_dir
+
+    sys.argv[1:] = remaining_argv
+
     unittest.main()