noxfile.py

@@ -173,8 +173,9 @@ def unit_tests(session: nox.Session):
     behave_cmd = session.bin + "/behave-parallel"
     parallel_args = _behave_parallel_args(session.posargs)
 
-    # If a specific feature file is passed, run only that file
-    if session.posargs and session.posargs[0].endswith(".feature"):
+    # If specific feature files are passed, run only those files
+    has_feature_files = any(arg.endswith(".feature") for arg in session.posargs)
+    if has_feature_files:
         args = [
             behave_cmd,
             "-q",
@@ -562,7 +563,8 @@ def coverage_report(session: nox.Session):
 
     # Build behave-parallel args (sequential for coverage).
     behave_cmd = session.bin + "/behave-parallel"
-    if session.posargs and session.posargs[0].endswith(".feature"):
+    has_feature_files = any(arg.endswith(".feature") for arg in session.posargs)
+    if has_feature_files:
         behave_args = [
             behave_cmd,
             "-q",

scripts/run_behave_parallel.py

@@ -337,7 +337,18 @@ def main(argv: list[str] | None = None) -> None:
 
     start = time.monotonic()
 
-    if processes <= 1 or coverage_mode or len(feature_paths) == 1:
+    # Run sequentially if:
+    # - processes <= 1 (explicitly requested)
+    # - coverage_mode (slipcover requires single process)
+    # - only 1 feature file (no parallelism benefit)
+    # - very few feature files relative to processes (fork overhead > benefit)
+    #   When feature_paths <= 2, sequential is faster and avoids fork deadlocks
+    if (
+        processes <= 1
+        or coverage_mode
+        or len(feature_paths) == 1
+        or len(feature_paths) <= 2
+    ):
         # ---- sequential in-process mode ----
         _, total = _run_features_inprocess(feature_paths, other_args)
     else: