implemented --last-failed-no-failures

_pytest/cacheprovider.py

@@ -112,11 +112,12 @@ class LFPlugin(object):
         self.active = any(config.getoption(key) for key in active_keys)
         self.lastfailed = config.cache.get("cache/lastfailed", {})
         self._previously_failed_count = None
+        self._no_failures_behavior = self.config.getoption('last_failed_no_failures')
 
     def pytest_report_collectionfinish(self):
         if self.active:
             if not self._previously_failed_count:
-                mode = "run all (no recorded failures)"
+                mode = "run {} (no recorded failures)".format(self._no_failures_behavior)
             else:
                 noun = 'failure' if self._previously_failed_count == 1 else 'failures'
                 suffix = " first" if self.config.getoption(
@@ -144,7 +145,8 @@ class LFPlugin(object):
             self.lastfailed[report.nodeid] = True
 
     def pytest_collection_modifyitems(self, session, config, items):
-        if self.active and self.lastfailed:
+        if self.active:
+            if self.lastfailed:
                 previously_failed = []
                 previously_passed = []
                 for item in items:
@@ -162,6 +164,9 @@ class LFPlugin(object):
                     config.hook.pytest_deselected(items=previously_passed)
                 else:
                     items[:] = previously_failed + previously_passed
+            elif self._no_failures_behavior == 'none':
+                config.hook.pytest_deselected(items=items)
+                items[:] = []
 
     def pytest_sessionfinish(self, session):
         config = self.config
@@ -230,6 +235,12 @@ def pytest_addoption(parser):
     parser.addini(
         "cache_dir", default='.pytest_cache',
         help="cache directory path.")
+    group.addoption(
+        '--lfnf', '--last-failed-no-failures', action='store',
+        dest='last_failed_no_failures', choices=('all', 'none'), default='all',
+        help='change the behavior when no test failed in the last run or no '
+             'information about the last failures was found in the cache'
+    )
 
 
 def pytest_cmdline_main(config):

changelog/3139.feature

@@ -0,0 +1 @@
+New ``--last-failed-no-failures`` command-line option that allows to specify the behavior of the cache plugin's ```--last-failed`` feature when no tests failed in the last run (or no cache was found): ``none`` or ``all`` (the default).

doc/en/cache.rst

@@ -156,6 +156,16 @@ New ``--nf``, ``--new-first`` options: run new tests first followed by the rest
 of the tests, in both cases tests are also sorted by the file modified time,
 with more recent files coming first.
 
+Behavior when no tests failed in the last run
+---------------------------------------------
+
+When no tests failed in the last run, or when no cached ``lastfailed`` data was
+found, ``pytest`` can be configured either to run all of the tests or no tests,
+using the ``--last-failed-no-failures`` option, which takes one of the following values::
+
+    pytest --last-failed-no-failures all    # run all tests (default behavior)
+    pytest --last-failed-no-failures none   # run no tests and exit
+
 The new config.cache object
 --------------------------------
 

testing/test_cacheprovider.py

@@ -604,6 +604,36 @@ class TestLastFailed(object):
         result.stdout.fnmatch_lines('*4 passed*')
         assert self.get_cached_last_failed(testdir) == []
 
+    def test_lastfailed_no_failures_behavior_all_passed(self, testdir):
+        testdir.makepyfile("""
+            def test_1():
+                assert True
+            def test_2():
+                assert True
+        """)
+        result = testdir.runpytest()
+        result.stdout.fnmatch_lines(["*2 passed*"])
+        result = testdir.runpytest("--lf")
+        result.stdout.fnmatch_lines(["*2 passed*"])
+        result = testdir.runpytest("--lf", "--lfnf", "all")
+        result.stdout.fnmatch_lines(["*2 passed*"])
+        result = testdir.runpytest("--lf", "--lfnf", "none")
+        result.stdout.fnmatch_lines(["*2 desel*"])
+
+    def test_lastfailed_no_failures_behavior_empty_cache(self, testdir):
+        testdir.makepyfile("""
+            def test_1():
+                assert True
+            def test_2():
+                assert False
+        """)
+        result = testdir.runpytest("--lf", "--cache-clear")
+        result.stdout.fnmatch_lines(["*1 failed*1 passed*"])
+        result = testdir.runpytest("--lf", "--cache-clear", "--lfnf", "all")
+        result.stdout.fnmatch_lines(["*1 failed*1 passed*"])
+        result = testdir.runpytest("--lf", "--cache-clear", "--lfnf", "none")
+        result.stdout.fnmatch_lines(["*2 desel*"])
+
 
 class TestNewFirst(object):
     def test_newfirst_usecase(self, testdir):