Add markers to linter tests, move linter imports

Test markers can be used to easily (de-)select tests, and colcon exposes
mechanisms to do so. Linters are a category of tests that are commonly
called out.

Additionally, if we move the imports for some of our single-purpose
tests into the test function, we can avoid installing the linter
dependencies entirely. This is a common case in platform packaging, where
linter errors are not actionable and the dependencies are not typically
installed.

setup.cfg

@@ -77,6 +77,9 @@ filterwarnings =
     # Suppress resource warnings pending investigation
     always::ResourceWarning
 junit_suite_name = colcon-core
+markers =
+    flake8
+    linter
 python_classes = !TestFailure
 
 [options.entry_points]

test/spell_check.words

@@ -53,6 +53,7 @@ junit
 levelname
 libexec
 lineno
+linter
 linux
 lstrip
 mkdtemp

test/test_copyright_license.py

@@ -4,7 +4,10 @@
 from pathlib import Path
 import sys
 
+import pytest
 
+
+@pytest.mark.linter
 def test_copyright_license():
     missing = check_files([
         Path(__file__).parents[1],

test/test_flake8.py

@@ -5,19 +5,20 @@
 from pathlib import Path
 import sys
 
-from flake8 import LOG
-from flake8.api.legacy import get_style_guide
-from pydocstyle.utils import log
+import pytest
 
 
-# avoid debug / info / warning messages from flake8 internals
-LOG.setLevel(logging.ERROR)
+@pytest.mark.flake8
+@pytest.mark.linter
+def test_flake8():
+    from flake8.api.legacy import get_style_guide
 
+    # avoid debug / info / warning messages from flake8 internals
+    logging.getLogger('flake8').setLevel(logging.ERROR)
 
-def test_flake8():
     # for some reason the pydocstyle logger changes to an effective level of 1
     # set higher level to prevent the output to be flooded with debug messages
-    log.setLevel(logging.WARNING)
+    logging.getLogger('pydocstyle').setLevel(logging.WARNING)
 
     style_guide = get_style_guide(
         extend_ignore=['D100', 'D104'],

test/test_spell_check.py

@@ -4,10 +4,6 @@
 from pathlib import Path
 
 import pytest
-from scspell import Report
-from scspell import SCSPELL_BUILTIN_DICT
-from scspell import spell_check
-
 
 spell_check_words_path = Path(__file__).parent / 'spell_check.words'
 
@@ -18,7 +14,12 @@ def known_words():
     return spell_check_words_path.read_text().splitlines()
 
 
+@pytest.mark.linter
 def test_spell_check(known_words):
+    from scspell import Report
+    from scspell import SCSPELL_BUILTIN_DICT
+    from scspell import spell_check
+
     source_filenames = [
         Path(__file__).parents[1] / 'bin' / 'colcon',
         Path(__file__).parents[1] / 'setup.py'] + \
@@ -46,11 +47,13 @@ def test_spell_check(known_words):
         ', '.join(sorted(unused_known_words))
 
 
+@pytest.mark.linter
 def test_spell_check_word_list_order(known_words):
     assert known_words == sorted(known_words), \
         'The word list should be ordered alphabetically'
 
 
+@pytest.mark.linter
 def test_spell_check_word_list_duplicates(known_words):
     assert len(known_words) == len(set(known_words)), \
         'The word list should not contain duplicates'