acceptance_test: clarify/document/fix tests

Ref: e2e6e31711 (r30863971)

testing/acceptance_test.py

@@ -12,6 +12,13 @@ import pytest
 from _pytest.main import EXIT_NOTESTSCOLLECTED, EXIT_USAGEERROR
 
 
+def prepend_pythonpath(*dirs):
+    cur = os.getenv("PYTHONPATH")
+    if cur:
+        dirs += (cur,)
+    return os.pathsep.join(str(p) for p in dirs)
+
+
 class TestGeneralUsage(object):
     def test_config_error(self, testdir):
         testdir.copy_example("conftest_usageerror/conftest.py")
@@ -570,14 +577,8 @@ class TestInvocationVariants(object):
         assert result.ret == 0
         result.stdout.fnmatch_lines(["*1 passed*"])
 
-        def join_pythonpath(what):
-            cur = os.environ.get("PYTHONPATH")
-            if cur:
-                return str(what) + os.pathsep + cur
-            return what
-
         empty_package = testdir.mkpydir("empty_package")
-        monkeypatch.setenv("PYTHONPATH", str(join_pythonpath(empty_package)))
+        monkeypatch.setenv("PYTHONPATH", str(empty_package), prepend=os.pathsep)
         # 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 +587,7 @@ class TestInvocationVariants(object):
         assert result.ret == 0
         result.stdout.fnmatch_lines(["*2 passed*"])
 
-        monkeypatch.setenv("PYTHONPATH", str(join_pythonpath(testdir)))
+        monkeypatch.setenv("PYTHONPATH", str(testdir), prepend=os.pathsep)
         result = testdir.runpytest("--pyargs", "tpkg.test_missing", syspathinsert=True)
         assert result.ret != 0
         result.stderr.fnmatch_lines(["*not*found*test_missing*"])
@@ -626,18 +627,13 @@ class TestInvocationVariants(object):
         #             ├── __init__.py
         #             └── test_world.py
 
-        def join_pythonpath(*dirs):
-            cur = os.environ.get("PYTHONPATH")
-            if cur:
-                dirs += (cur,)
-            return os.pathsep.join(str(p) for p in dirs)
-
-        monkeypatch.setenv("PYTHONPATH", join_pythonpath(*search_path))
+        # NOTE: the different/reversed ordering is intentional here.
+        monkeypatch.setenv("PYTHONPATH", prepend_pythonpath(*search_path))
         for p in search_path:
             monkeypatch.syspath_prepend(p)
 
         # mixed module and filenames:
-        os.chdir("world")
+        monkeypatch.chdir("world")
         result = testdir.runpytest("--pyargs", "-v", "ns_pkg.hello", "ns_pkg/world")
         assert result.ret == 0
         result.stdout.fnmatch_lines(
@@ -688,8 +684,6 @@ class TestInvocationVariants(object):
                 pytest.skip(six.text_type(e.args[0]))
         monkeypatch.delenv("PYTHONDONTWRITEBYTECODE", raising=False)
 
-        search_path = ["lib", os.path.join("local", "lib")]
-
         dirname = "lib"
         d = testdir.mkdir(dirname)
         foo = d.mkdir("foo")
@@ -722,13 +716,9 @@ class TestInvocationVariants(object):
         #             ├── conftest.py
         #             └── test_bar.py
 
-        def join_pythonpath(*dirs):
-            cur = os.getenv("PYTHONPATH")
-            if cur:
-                dirs += (cur,)
-            return os.pathsep.join(str(p) for p in dirs)
-
-        monkeypatch.setenv("PYTHONPATH", join_pythonpath(*search_path))
+        # NOTE: the different/reversed ordering is intentional here.
+        search_path = ["lib", os.path.join("local", "lib")]
+        monkeypatch.setenv("PYTHONPATH", prepend_pythonpath(*search_path))
         for p in search_path:
             monkeypatch.syspath_prepend(p)