tests: improve test_config.py timing and behavior

Instead of bothering to create a proper west init-based installation
when testing the configuration commands, use a fixture that just
creates what is needed, and also validates module-wide assumptions
instead of repeating them in each test case.

This improves the quality of the test by only testing what is needed,
helping to isolate these tests from unrelated errors in the manifest
handling code.

It also drops the test time from ~3.5 seconds to about ~2.5 seconds in
my Linux environment.

Signed-off-by: Marti Bolivar <marti.bolivar@nordicsemi.no>

tests/test_config.py

@@ -2,16 +2,7 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
-#
-# Test cases
-#
-# For some tests cases, the environment setting HOME must be redirected to a
-# tmp folder.
-# This is configured in tox.ini to ensure tests can run without modifying the
-# settings of the calling user.
-# If running this test directly using pytest, those tests will be skipped.
-#
-
+import configparser
 import os
 import subprocess
 
@@ -22,23 +13,38 @@ from west.util import canon_path
 
 from conftest import cmd
 
-
-# We skip this test if executed directly using pytest, to avoid modifying
-# user's real ~/.westconfig.
-# We want to ensure HOME is pointing inside TOX temp dir before continuing.
-@pytest.mark.skipif(os.environ.get('TOXTEMPDIR') is None,
-                    reason="This test requires to be executed using tox")
-def test_config_global(west_init_tmpdir):
-    if not os.path.exists(os.path.expanduser('~')):
-        os.mkdir(os.path.expanduser('~'))
-
-    # To ensure that GLOBAL home folder points into tox temp dir.
-    # Otherwise fail the test, as we don't want to risk manipulating user's
-    # west config
+@pytest.fixture
+def config_tmpdir(tmpdir):
+    # Fixture for running from a temporary directory with a .west
+    # inside. We also:
+    #
+    # - ensure we're being run under tox, to avoid messing with
+    #   the user's actual configuration files
+    # - ensure configuration files point where they should inside
+    #   the temporary tox directories, for the same reason
+    # - ensure ~ exists (since the test environment
+    #   doesn't let us run in the true user $HOME).
+    # - set ZEPHYR_BASE (to avoid complaints in subcommand stderr)
+    #
+    # Using this makes the tests run faster than if we used
+    # west_init_tmpdir from conftest.py, and also ensures that the
+    # configuration code doesn't depend on features like the existence
+    # of a manifest file, helping separate concerns.
+    assert 'TOXTEMPDIR' in os.environ, 'you must run tests using tox'
     assert canon_path(config.ConfigFile.GLOBAL.value) == \
         canon_path(os.path.join(os.environ.get('TOXTEMPDIR'),
                                 'pytest-home', '.westconfig'))
+    if not os.path.exists(os.path.expanduser('~')):
+        os.mkdir(os.path.expanduser('~'))
+    os.environ['ZEPHYR_BASE'] = str(tmpdir.join('no-zephyr-here'))
+    tmpdir.mkdir('.west')
+    tmpdir.chdir()
 
+def cfg_obj():
+    return configparser.ConfigParser(allow_no_value=True)
+
+
+def test_config_global(config_tmpdir):
     # Make sure the value is currently unset.
     testkey_value = cmd('config pytest.testkey_global')
     assert testkey_value == ''
@@ -63,10 +69,7 @@ def test_config_global(west_init_tmpdir):
     testkey_value = cmd('config pytest.testkey_global')
     assert testkey_value.rstrip() == 'foo'
 
-def test_config_local(west_init_tmpdir):
-    if not os.path.exists(os.path.expanduser('~')):
-        os.mkdir(os.path.expanduser('~'))
-
+def test_config_local(config_tmpdir):
     testkey_value = cmd('config pytest.testkey_local')
     assert testkey_value == ''
 
@@ -107,15 +110,7 @@ def test_config_local(west_init_tmpdir):
     testkey_value = cmd('config pytest.testkey_local')
     assert testkey_value.rstrip() == 'foo2'
 
-# We skip this test if executed directly using pytest, to avoid modifying
-# user's real ~/.westconfig.
-# We want to ensure HOME is pointing inside TOX temp dir before continuing.
-@pytest.mark.skipif(os.environ.get('TOXTEMPDIR') is None,
-                    reason="This test requires to be executed using tox")
-def test_config_precedence(west_init_tmpdir):
-    if not os.path.exists(os.path.expanduser('~')):
-        os.mkdir(os.path.expanduser('~'))
-
+def test_config_precedence(config_tmpdir):
     # Make sure the value is not set.
     testkey_value = cmd('config pytest.testkey_precedence')
     assert testkey_value == ''
@@ -143,11 +138,7 @@ def test_config_precedence(west_init_tmpdir):
     testkey_value = cmd('config --global pytest.testkey_precedence')
     assert testkey_value.rstrip() == 'foo_global'
 
-
-def test_config_missing_key(west_init_tmpdir):
-    if not os.path.exists(os.path.expanduser('~')):
-        os.mkdir(os.path.expanduser('~'))
-
+def test_config_missing_key(config_tmpdir):
     with pytest.raises(subprocess.CalledProcessError) as e:
         cmd('config pytest')
         assert str(e) == 'west config: error: missing key, please invoke ' \