Improve automated tests support on Windows

noxfile.py

@@ -40,7 +40,13 @@ def tests(session):
         session.run("pytest", *tests)
         return
     session.run(
-        "pytest", "--cov=nox", "--cov-config", ".coveragerc", "--cov-report=", *tests
+        "pytest",
+        "--cov=nox",
+        "--cov-config",
+        ".coveragerc",
+        "--cov-report=",
+        *tests,
+        env={"COVERAGE_FILE": ".coverage.{}".format(session.python)}
     )
     session.notify("cover")
 
@@ -65,6 +71,7 @@ def cover(session):
         return
 
     session.install("coverage")
+    session.run("coverage", "combine")
     session.run("coverage", "report", "--fail-under=100", "--show-missing")
     session.run("coverage", "erase")
 
@@ -94,7 +101,7 @@ def lint(session):
     session.run("flake8", "nox", *files)
 
 
-@nox.session(python="3.8")
+@nox.session(python="3.7")
 def docs(session):
     """Build the documentation."""
     output_dir = os.path.join(session.create_tmp(), "output")

tests/test_virtualenv.py

@@ -181,13 +181,18 @@ def test_condaenv_create(make_conda):
     assert dir_.join("test.txt").check()
 
 
-@pytest.mark.skipif(IS_WINDOWS, reason="Not testing multiple interpreters on Windows.")
 @pytest.mark.skipif(not HAS_CONDA, reason="Missing conda command.")
 def test_condaenv_create_interpreter(make_conda):
     venv, dir_ = make_conda(interpreter="3.7")
     venv.create()
-    assert dir_.join("bin", "python").check()
-    assert dir_.join("bin", "python3.7").check()
+    if IS_WINDOWS:
+        assert dir_.join("python.exe").check()
+        assert dir_.join("python37.dll").check()
+        assert dir_.join("python37.pdb").check()
+        assert not dir_.join("python37.exe").check()
+    else:
+        assert dir_.join("bin", "python").check()
+        assert dir_.join("bin", "python3.7").check()
 
 
 @mock.patch("nox.virtualenv._SYSTEM", new="Windows")