chore: allow running dragonfly pytests in repeat (#3577)

tests/README.md

@@ -19,6 +19,7 @@ You can override the location of the binary using `DRAGONFLY_PATH` environment v
 - use `--log-seeder file` to store all single-db commands from the lastest tests seeder inside file.
 - use `--existing-port` to use an existing instance for tests instead of starting one
 - use `--rand-seed` to set the global random seed. Makes the seeder predictable.
+- use `--repeat <N>` to run a test multiple times.
 
 for example,
 

tests/dragonfly/conftest.py

@@ -276,6 +276,22 @@ def pytest_addoption(parser):
         default=None,
         help="Provide a port to the existing memcached process for the test",
     )
+    parser.addoption("--repeat", action="store", help="Number of times to repeat each test")
+
+
+def pytest_generate_tests(metafunc):
+    if metafunc.config.option.repeat is not None:
+        count = int(metafunc.config.option.repeat)
+
+        # We're going to duplicate these tests by parametrizing them,
+        # which requires that each test has a fixture to accept the parameter.
+        # We can add a new fixture like so:
+        metafunc.fixturenames.append("tmp_ct")
+
+        # Now we parametrize. This is what happens when we do e.g.,
+        # @pytest.mark.parametrize('tmp_ct', range(count))
+        # def test_foo(): pass
+        metafunc.parametrize("tmp_ct", range(count))
 
 
 @pytest.fixture(scope="session")