Fix ZeroDivisionError with 0 collected tests

_pytest/terminal.py

@@ -313,8 +313,11 @@ def _write_progress_if_past_edge(self):
     _PROGRESS_LENGTH = len(' [100%]')
 
     def _get_progress_information_message(self):
-        progress = self._progress_items_reported * 100 // self._session.testscollected
-        return ' [{:3d}%]'.format(progress)
+        collected = self._session.testscollected
+        if collected:
+            progress = self._progress_items_reported * 100 // collected
+            return ' [{:3d}%]'.format(progress)
+        return ' [100%]'
 
     def _write_progress_information_filling_space(self):
         if not self._show_progress_info:

changelog/2971.bugfix

@@ -0,0 +1 @@
+Fix ``ZeroDivisionError`` when using the ``testmon`` plugin when no tests were actually collected.

testing/test_terminal.py

@@ -988,6 +988,24 @@ def test_foobar(i): pass
             """,
         )
 
+    def test_zero_tests_collected(self, testdir):
+        """Some plugins (testmon for example) might issue pytest_runtest_logreport without any tests being
+        actually collected (#2971)."""
+        testdir.makeconftest("""
+        def pytest_collection_modifyitems(items, config):
+            from _pytest.runner import CollectReport
+            for node_id in ('nodeid1', 'nodeid2'):
+                rep = CollectReport(node_id, 'passed', None, None)
+                rep.when = 'passed'
+                rep.duration = 0.1
+                config.hook.pytest_runtest_logreport(report=rep)
+        """)
+        output = testdir.runpytest()
+        assert 'ZeroDivisionError' not in output.stdout.str()
+        output.stdout.fnmatch_lines([
+            '=* 2 passed in *=',
+        ])
+
     def test_normal(self, many_tests_file, testdir):
         output = testdir.runpytest()
         output.stdout.re_match_lines([