Show a warning when non-str is given to Monkeypatch.setenv

src/_pytest/monkeypatch.py

@@ -225,7 +225,15 @@ class MonkeyPatch(object):
         """ Set environment variable ``name`` to ``value``.  If ``prepend``
         is a character, read the current environment variable value
         and prepend the ``value`` adjoined with the ``prepend`` character."""
-        value = str(value)
+        if not isinstance(value, str):
+            warnings.warn(
+                pytest.PytestWarning(
+                    "Environment variable value {!r} should be str, converted to str implicitly".format(
+                        value
+                    )
+                )
+            )
+            value = str(value)
         if prepend and name in os.environ:
             value = value + prepend + os.environ[name]
         self._warn_if_env_name_is_not_str(name)

testing/acceptance_test.py

@@ -577,7 +577,7 @@ class TestInvocationVariants(object):
             return what
 
         empty_package = testdir.mkpydir("empty_package")
-        monkeypatch.setenv("PYTHONPATH", join_pythonpath(empty_package))
+        monkeypatch.setenv("PYTHONPATH", str(join_pythonpath(empty_package)))
         # the path which is not a package raises a warning on pypy;
         # no idea why only pypy and not normal python warn about it here
         with warnings.catch_warnings():
@@ -586,7 +586,7 @@ class TestInvocationVariants(object):
         assert result.ret == 0
         result.stdout.fnmatch_lines(["*2 passed*"])
 
-        monkeypatch.setenv("PYTHONPATH", join_pythonpath(testdir))
+        monkeypatch.setenv("PYTHONPATH", str(join_pythonpath(testdir)))
         result = testdir.runpytest("--pyargs", "tpkg.test_missing", syspathinsert=True)
         assert result.ret != 0
         result.stderr.fnmatch_lines(["*not*found*test_missing*"])

testing/test_cacheprovider.py

@@ -215,7 +215,7 @@ def test_cache_show(testdir):
 
 class TestLastFailed(object):
     def test_lastfailed_usecase(self, testdir, monkeypatch):
-        monkeypatch.setenv("PYTHONDONTWRITEBYTECODE", 1)
+        monkeypatch.setenv("PYTHONDONTWRITEBYTECODE", "1")
         p = testdir.makepyfile(
             """
             def test_1():
@@ -301,7 +301,7 @@ class TestLastFailed(object):
         assert "test_a.py" not in result.stdout.str()
 
     def test_lastfailed_difference_invocations(self, testdir, monkeypatch):
-        monkeypatch.setenv("PYTHONDONTWRITEBYTECODE", 1)
+        monkeypatch.setenv("PYTHONDONTWRITEBYTECODE", "1")
         testdir.makepyfile(
             test_a="""\
             def test_a1():
@@ -335,7 +335,7 @@ class TestLastFailed(object):
         result.stdout.fnmatch_lines(["*1 failed*1 desel*"])
 
     def test_lastfailed_usecase_splice(self, testdir, monkeypatch):
-        monkeypatch.setenv("PYTHONDONTWRITEBYTECODE", 1)
+        monkeypatch.setenv("PYTHONDONTWRITEBYTECODE", "1")
         testdir.makepyfile(
             """\
             def test_1():
@@ -474,8 +474,8 @@ class TestLastFailed(object):
         )
 
         def rlf(fail_import, fail_run):
-            monkeypatch.setenv("FAILIMPORT", fail_import)
+            monkeypatch.setenv("FAILIMPORT", str(fail_import))
-            monkeypatch.setenv("FAILTEST", fail_run)
+            monkeypatch.setenv("FAILTEST", str(fail_run))
 
             testdir.runpytest("-q")
             config = testdir.parseconfigure()
@@ -519,8 +519,8 @@ class TestLastFailed(object):
         )
 
         def rlf(fail_import, fail_run, args=()):
-            monkeypatch.setenv("FAILIMPORT", fail_import)
+            monkeypatch.setenv("FAILIMPORT", str(fail_import))
-            monkeypatch.setenv("FAILTEST", fail_run)
+            monkeypatch.setenv("FAILTEST", str(fail_run))
 
             result = testdir.runpytest("-q", "--lf", *args)
             config = testdir.parseconfigure()

testing/test_junitxml.py

@@ -850,7 +850,7 @@ def test_logxml_path_expansion(tmpdir, monkeypatch):
     assert xml_tilde.logfile == home_tilde
 
     # this is here for when $HOME is not set correct
-    monkeypatch.setenv("HOME", tmpdir)
+    monkeypatch.setenv("HOME", str(tmpdir))
     home_var = os.path.normpath(os.path.expandvars("$HOME/test.xml"))
 
     xml_var = LogXML("$HOME%stest.xml" % tmpdir.sep, None)

testing/test_monkeypatch.py

@@ -165,7 +165,8 @@ def test_delitem():
 
 def test_setenv():
     monkeypatch = MonkeyPatch()
-    monkeypatch.setenv("XYZ123", 2)
+    with pytest.warns(pytest.PytestWarning):
+        monkeypatch.setenv("XYZ123", 2)
     import os
 
     assert os.environ["XYZ123"] == "2"
@@ -194,15 +195,16 @@ def test_delenv():
             del os.environ[name]
 
 
-@pytest.mark.skipif(six.PY3, reason="Python 2 only test")
+class TestEnvironWarnings(object):
-class TestEnvironKeysWarning(object):
     """
-    os.environ needs keys to be native strings, otherwise it will cause problems with other modules (notably
+    os.environ keys and values should be native strings, otherwise it will cause problems with other modules (notably
-    subprocess). We only test this behavior on Python 2, because Python 3 raises an error right away.
+    subprocess). On Python 2 os.environ accepts anything without complaining, while Python 3 does the right thing
+    and raises an error.
     """
 
     VAR_NAME = u"PYTEST_INTERNAL_MY_VAR"
 
+    @pytest.mark.skipif(six.PY3, reason="Python 2 only test")
     def test_setenv_unicode_key(self, monkeypatch):
         with pytest.warns(
             pytest.PytestWarning,
@@ -210,6 +212,7 @@ class TestEnvironKeysWarning(object):
         ):
             monkeypatch.setenv(self.VAR_NAME, "2")
 
+    @pytest.mark.skipif(six.PY3, reason="Python 2 only test")
     def test_delenv_unicode_key(self, monkeypatch):
         with pytest.warns(
             pytest.PytestWarning,
@@ -217,14 +220,24 @@ class TestEnvironKeysWarning(object):
         ):
             monkeypatch.delenv(self.VAR_NAME, raising=False)
 
+    def test_setenv_non_str_warning(self, monkeypatch):
+        value = 2
+        msg = (
+            "Environment variable value {!r} should be str, converted to str implicitly"
+        )
+        with pytest.warns(pytest.PytestWarning, match=msg.format(value)):
+            monkeypatch.setenv(str(self.VAR_NAME), value)
+
 
 def test_setenv_prepend():
     import os
 
     monkeypatch = MonkeyPatch()
-    monkeypatch.setenv("XYZ123", 2, prepend="-")
+    with pytest.warns(pytest.PytestWarning):
+        monkeypatch.setenv("XYZ123", 2, prepend="-")
     assert os.environ["XYZ123"] == "2"
-    monkeypatch.setenv("XYZ123", 3, prepend="-")
+    with pytest.warns(pytest.PytestWarning):
+        monkeypatch.setenv("XYZ123", 3, prepend="-")
     assert os.environ["XYZ123"] == "3-2"
     monkeypatch.undo()
     assert "XYZ123" not in os.environ