tests: check that PYTEST_ADDOPTS is not processed twice

Ref: pytest-dev/pytest#6008

Regressed in 953a3f0, uncovering a bug in pytest.

changelog/478.bugfix.rst

@@ -0,0 +1 @@
+Fix regression with duplicated arguments via $PYTEST_ADDOPTS in 1.30.0.

testing/acceptance_test.py

@@ -590,7 +590,7 @@ def test_hello(myarg):
     assert result.ret
 
 
-def test_config_initialization(testdir, pytestconfig):
+def test_config_initialization(testdir, monkeypatch, pytestconfig):
     """Ensure workers and master are initialized consistently. Integration test for #445"""
     if not hasattr(pytestconfig, "invocation_params"):
         pytest.skip(
@@ -599,7 +599,8 @@ def test_config_initialization(testdir, pytestconfig):
     testdir.makepyfile(
         **{
             "dir_a/test_foo.py": """
-                def test_1(): pass
+                def test_1(request):
+                    assert request.config.option.verbose == 2
         """
         }
     )
@@ -610,8 +611,10 @@ def test_1(): pass
         testpaths=dir_a
     """,
     )
+    monkeypatch.setenv("PYTEST_ADDOPTS", "-v")
     result = testdir.runpytest("-n2", "-c", "myconfig.ini", "-v")
-    result.stdout.fnmatch_lines(["dir_a/test_foo.py::test_1*"])
+    result.stdout.fnmatch_lines(["dir_a/test_foo.py::test_1*", "*= 1 passed in *"])
+    assert result.ret == 0
 
 
 @pytest.mark.parametrize("when", ["setup", "call", "teardown"])