feat: warnings are now real warnings

This makes coverage warnings visible when running test suites under
pytest.  But it also means some uninteresting warnings would show up in
our own test suite, so we had to catch or suppress those.

1 files changed, 13 insertions, 10 deletions

diff --git a/tests/test_plugins.py b/tests/test_plugins.py
index 3401895b..b15ee45b 100644
--- a/tests/test_plugins.py
+++ b/tests/test_plugins.py
@@ -14,7 +14,7 @@ import coverage
 from coverage import env
 from coverage.control import Plugins
 from coverage.data import line_counts
-from coverage.exceptions import CoverageException
+from coverage.exceptions import CoverageException, CoverageWarning
 from coverage.misc import import_local_file
 
 import coverage.plugin
@@ -193,7 +193,9 @@ class PluginTest(CoverageTest):
         cov = coverage.Coverage(debug=["sys"])
         cov._debug_file = debug_out
         cov.set_option("run:plugins", ["plugin_sys_info"])
-        cov.start()
+        with pytest.warns(None):
+            # Catch warnings so we don't see "plugins aren't supported on PyTracer"
+            cov.start()
         cov.stop()      # pragma: nested
 
         out_lines = [line.strip() for line in debug_out.getvalue().splitlines()]
@@ -631,28 +633,29 @@ class BadFileTracerTest(FileTracerTest):
         explaining why.
 
         """
-        self.run_plugin(module_name)
+        with pytest.warns(Warning) as warns:
+            self.run_plugin(module_name)
 
         stderr = self.stderr()
-
+        stderr += "".join(w.message.args[0] for w in warns)
         if our_error:
-            errors = stderr.count("# Oh noes!")
             # The exception we're causing should only appear once.
-            assert errors == 1
+            assert stderr.count("# Oh noes!") == 1
 
         # There should be a warning explaining what's happening, but only one.
         # The message can be in two forms:
         #   Disabling plug-in '...' due to previous exception
         # or:
         #   Disabling plug-in '...' due to an exception:
-        msg = f"Disabling plug-in '{module_name}.{plugin_name}' due to "
-        warnings = stderr.count(msg)
-        assert warnings == 1
+        assert len(warns) == 1
+        assert issubclass(warns[0].category, CoverageWarning)
+        warnmsg = warns[0].message.args[0]
+        assert f"Disabling plug-in '{module_name}.{plugin_name}' due to " in warnmsg
 
         if excmsg:
             assert excmsg in stderr
         if excmsgs:
-            assert any(em in stderr for em in excmsgs), "expected one of %r" % excmsgs
+            assert any(em in stderr for em in excmsgs), f"expected one of {excmsgs} in stderr"
 
     def test_file_tracer_has_no_file_tracer_method(self):
         self.make_file("bad_plugin.py", """\