Remove --randomly-repeat-last in favour of --randomly-seed=last

Change the design from #164.

HISTORY.rst

@@ -8,6 +8,9 @@ Pending Release
 
 .. Insert new release notes below this line
 
+* Add the option ``--randomly-seed=last`` to reuse the last used value for the
+  seed.
+
 2.0.0 (2019-02-28)
 ------------------
 

README.rst

@@ -85,6 +85,12 @@ them with that seed using the flag as suggested:
 
     pytest --randomly-seed=1234
 
+Or more conveniently, use the special value ``last``:
+
+.. code-block:: bash
+
+    pytest --randomly-seed=last
+
 Since the ordering is by module, then by class, you can debug inter-test
 pollution failures by narrowing down which tests are being run to find the bad
 interaction by rerunning just the module/class:

pytest_randomly.py

@@ -1,3 +1,4 @@
+import argparse
 import random
 import time
 
@@ -31,17 +32,29 @@
 __version__ = '2.0.0'
 
 
+default_seed = int(time.time())
+
+
+def seed_type(string):
+    if string == 'last':
+        return string
+    try:
+        return int(string)
+    except ValueError:
+        raise argparse.ArgumentTypeError(
+            "{} is not an integer or the string 'last'".format(repr(string))
+        )
+
+
 def pytest_addoption(parser):
     group = parser.getgroup('randomly', 'Randomizes tests')
-    group._addoption(
-        '--randomly-repeat-last', action='store_true', dest='randomly_repeat_last',
-        help="""Set the seed to the previous run's seed."""
-    )
     group._addoption(
         '--randomly-seed', action='store', dest='randomly_seed',
-        default=int(time.time()), type=int,
-        help="""Set the seed that pytest-randomly uses. Default behaviour:
-                use time.time()"""
+        default=str(default_seed), type=seed_type,
+        help="""Set the seed that pytest-randomly uses (int), or pass the
+                special value 'last' to reuse the seed from the previous run.
+                Default behaviour: use int(time.time()), so the seed is
+                different on each run."""
     )
     group._addoption(
         '--randomly-dont-reset-seed', action='store_false',
@@ -83,18 +96,15 @@ def _reseed(config, offset=0):
             np_random.set_state(np_random_states[seed])
 
 
-def pytest_configure(config):
-    if config.option.randomly_repeat_last and config.cache.get('last_seed', None):
-        seed = config.cache.get('last_seed', None)
+def pytest_report_header(config):
+    seed_value = config.getoption('randomly_seed')
+    if seed_value == 'last':
+        seed = config.cache.get('randomly_seed', default_seed)
     else:
-        seed = config.getoption('randomly_seed')
-    config.cache.set('last_seed', seed)
+        seed = seed_value
+    config.cache.set('randomly_seed', seed)
     config.option.randomly_seed = seed
-
-
-def pytest_report_header(config):
     _reseed(config)
-    seed = config.getoption('randomly_seed')
     return "Using --randomly-seed={0}".format(seed)
 
 

tests/test_it.py

@@ -70,38 +70,50 @@ def test_b():
     out.assert_outcomes(passed=2, failed=0)
 
 
-def test_it_reuses_the_prev_run_seed(ourtestdir):
-    """
-    Run a test that exercises the randomly-repeat-last option.
-    """
+def test_using_last_seed(ourtestdir):
     ourtestdir.makepyfile(
         test_one="""
         def test_a():
             pass
         """
     )
-    out = ourtestdir.runpytest('--randomly-seed=33')
+    out = ourtestdir.runpytest()
     out.assert_outcomes(passed=1, failed=0)
-    out.stdout.fnmatch_lines(['Using --randomly-seed=33'])
+    seed_line = [x for x in out.stdout.lines if x.startswith('Using --randomly-seed=')][0]
+
+    out = ourtestdir.runpytest('--randomly-seed=last')
+    out.assert_outcomes(passed=1, failed=0)
+    out.stdout.fnmatch_lines([seed_line])
+
+
+def test_using_last_explicit_seed(ourtestdir):
     ourtestdir.makepyfile(
         test_one="""
         def test_a():
             pass
         """
     )
-    out = ourtestdir.runpytest('--randomly-repeat-last')
+    out = ourtestdir.runpytest('--randomly-seed=33')
+    out.assert_outcomes(passed=1, failed=0)
+    out.stdout.fnmatch_lines(['Using --randomly-seed=33'])
+
+    out = ourtestdir.runpytest('--randomly-seed=last')
     out.assert_outcomes(passed=1, failed=0)
     out.stdout.fnmatch_lines(['Using --randomly-seed=33'])
+
+
+def test_passing_nonsense_for_randomly_seed(ourtestdir):
     ourtestdir.makepyfile(
         test_one="""
         def test_a():
             pass
         """
     )
-    out = ourtestdir.runpytest()
-    out.assert_outcomes(passed=1, failed=0)
-    for line in out.outlines:
-        assert 'Using --randomly-seed=33' not in line
+    out = ourtestdir.runpytest('--randomly-seed=invalidvalue')
+    assert out.ret != 0
+    out.stderr.fnmatch_lines([
+        "pytest.py: error: argument --randomly-seed: 'invalidvalue' is not an integer or the string 'last'"
+    ])
 
 
 def test_it_resets_the_random_seed_at_the_start_of_test_classes(ourtestdir):