test.py: fix test collection bug

In certain circumstances current way of collecting can be error prone.
Collection can stop when the first file is skipped in the mode leaving
the rest of the files in CLI not collected.
Another issue that if the file specified twice, with directory and file
explicitly, it will produce incorrect CppFile in the stash causing
KeyError.

Fixes: https://scylladb.atlassian.net/browse/SCYLLADB-1714

test/pylib/cpp/base.py

@@ -126,6 +126,9 @@ class CppFile(pytest.File, ABC):
         return args
 
     def collect(self) -> Iterator[CppTestCase]:
+        if BUILD_MODE not in self.stash:
+            return
+
         custom_args = self.suite_config.get("custom_args", {}).get(self.test_name, DEFAULT_CUSTOM_ARGS)
 
         for test_case in self.list_test_cases():

test/pylib/runner.py

@@ -163,6 +163,11 @@ def scylla_binary(testpy_test) -> Path:
 
 
 def pytest_collection_modifyitems(items: list[pytest.Item]) -> None:
+    items[:] = [
+        item for item in items
+        if (parent_file := item.getparent(cls=pytest.File)) is not None
+           and BUILD_MODE in parent_file.stash
+    ]
     for item in items:
         modify_pytest_item(item=item)
 
@@ -340,7 +345,8 @@ def pytest_collect_file(file_path: pathlib.Path,
         repeats = list(product(build_modes, parent.config.run_ids))
 
         if not repeats:
-            return []
+            parent.stash[REPEATING_FILES].remove(file_path)
+            return collectors
 
         ihook = parent.ihook
         collectors = list(chain(collectors, chain.from_iterable(