feature: add the option --randomly-seed-per-test to use a different seed for each test

Author: brycedrennan

CHANGELOG.rst

@@ -2,6 +2,13 @@
 Changelog
 =========
 
+3.16.0 (2024-04-09)
+-------------------
+
+* Add the option ``--randomly-seed-per-test`` to use a different seed for each test.
+
+  Resolves `Issue #600 <https://github.com/pytest-dev/pytest-randomly/issues/600>`__
+
 3.15.0 (2023-08-15)
 -------------------
 

README.rst

@@ -160,6 +160,9 @@ You can disable behaviours you don't like with the following flags:
   the start of every test
 * ``--randomly-dont-reorganize`` - turn off the shuffling of the order of tests
 
+By default each test starts out with the same seed, if you'd like a different one
+per test you can use the ``--randomly-seed-per-test`` flag.
+
 The plugin appears to Pytest with the name 'randomly'. To disable it
 altogether, you can use the ``-p`` argument, for example:
 

src/pytest_randomly/__init__.py

@@ -95,6 +95,15 @@ def pytest_addoption(parser: Parser) -> None:
                 Default behaviour: use random.Random().getrandbits(32), so the seed is
                 different on each run.""",
     )
+    group._addoption(
+        "--randomly-seed-per-test",
+        action="store_true",
+        dest="randomly_seed_per_test",
+        default=False,
+        help="""Use a different seed for each test. Can be helpful for getting
+                different random data in each test, but still having reproducible
+                tests. Default behaviour: False.""",
+    )
     group._addoption(
         "--randomly-dont-reset-seed",
         action="store_false",
@@ -209,9 +218,17 @@ def pytest_runtest_setup(item: Item) -> None:
         _reseed(item.config, -1)
 
 
+def seed_from_string(string: str) -> int:
+    return int(hashlib.md5(string.encode()).hexdigest(), 16)
+
+
 def pytest_runtest_call(item: Item) -> None:
     if item.config.getoption("randomly_reset_seed"):
-        _reseed(item.config)
+        if item.config.getoption("randomly_seed_per_test"):
+            test_offset = seed_from_string(item.nodeid) + 100
+        else:
+            test_offset = 0
+        _reseed(item.config, offset=test_offset)
 
 
 def pytest_runtest_teardown(item: Item) -> None:

tests/test_pytest_randomly.py

@@ -82,6 +82,29 @@ def test_b():
     out.assert_outcomes(passed=2, failed=0)
 
 
+def test_it_can_use_different_random_seed_per_test(ourtester):
+    """
+    Run a pair of tests that generate a number and assert they produce different numbers.
+    """
+    ourtester.makepyfile(
+        test_one="""
+        import random
+
+        def test_a():
+            test_a.num = random.random()
+            if hasattr(test_b, 'num'):
+                assert test_a.num != test_b.num
+
+        def test_b():
+            test_b.num = random.random()
+            if hasattr(test_a, 'num'):
+                assert test_b.num != test_a.num
+        """
+    )
+    out = ourtester.runpytest("--randomly-seed-per-test")
+    out.assert_outcomes(passed=2, failed=0)
+
+
 def test_without_cacheprovider(ourtester):
     ourtester.makepyfile(
         test_one="""