Ensure --dist=loadscope is used when running pytest

The loadscope setting is required for parallel execution of our system
tests using pytest. To ensure it's always used, place it in pytest.ini.
This has a slight downside that pytest-xdist must still be installed
even when attempting to execute tests with pytest sequentially.

Author: nicki-krizek

bin/tests/system/README

@@ -97,12 +97,7 @@ Issuing plain `pytest` command without any argument will execute all tests
 sequenatially. To execute them in parallel, ensure you have pytest-xdist
 installed and run:
 
-pytest --dist loadscope -n <number-of-workers>
-
-It is vital to provide the `--dist loadscope` option when running the tests in
-parallel to ensure tests from a single module are executed from the same
-thread. Otherwise, there's a risk of port contention and inefficient use of
-resources.
+pytest -n <number-of-workers>
 
 
 Running the System Tests Using the Legacy Runner
@@ -706,9 +701,10 @@ Pytest-xdist is used for executing pytest test cases in parallel using the `-n
 N_WORKERS` option. By default, xdist will distribute any test case to any
 worker, which would lead to the issue described above. Therefore, it is vital
 to use the `--dist loadscope` option which ensures that test cases within the
-same (module) scope will be handled by the same worker.
+same (module) scope will be handled by the same worker. This option has been
+added to pytest.ini so it doesn't need to be specified on the command line.
 
-$ pytest -n 4 --dist loadscope
+$ pytest -n 4
 
 Test selection
 ---

bin/tests/system/pytest.ini

@@ -10,7 +10,7 @@
 # information regarding copyright ownership.
 
 [pytest]
-addopts = --tb=short -rA
+addopts = --tb=short -rA --dist loadscope
 log_format = %(asctime)s %(levelname)s:%(name)s %(message)s
 log_date_format = %Y-%m-%d %H:%M:%S
 log_cli = 1

bin/tests/system/run.sh

@@ -28,7 +28,6 @@ def into_pytest_args(in_args):
     if in_args.expression is None:
         # running all tests - execute in parallel
         args.extend(["-n", "4"])
-        args.extend(["--dist", "loadscope"])
     else:
         args.extend(["-k", in_args.expression])
     if in_args.noclean:
@@ -48,7 +47,7 @@ def main():
         "Using pytest system test runner\n\n"
         'Please consider invoking "pytest" directly for more control:\n'
         "  single test:     pytest -k dns64\n"
-        "  parallel tests:  pytest -n 4 --dist loadscope\n\n"
+        "  parallel tests:  pytest -n 4\n\n"
         "Alternately, use ./legacy.run.sh for the legacy system test runner.\n"
     )