test: support skip running linters via env variable

Support skip running the linters by setting the environment variable
`SKIP_LINTERS=1`. This flag is useful for distributions.

tests/test_black.py

@@ -14,6 +14,7 @@
 
 """Run black code formatter in check mode."""
 
+import os
 import subprocess
 import sys
 import unittest
@@ -28,6 +29,7 @@ class BlackTestCase(unittest.TestCase):
     source files is provided by the get_source_files() function.
     """
 
+    @unittest.skipIf(os.environ.get("SKIP_LINTERS"), "requested via SKIP_LINTERS env variable")
     def test_black(self):
         """Test: Run black code formatter on Python source code."""
 

tests/test_flake8.py

@@ -14,6 +14,7 @@
 
 """Run flake8 check."""
 
+import os
 import subprocess
 import sys
 import unittest
@@ -29,6 +30,7 @@ class Flake8TestCase(unittest.TestCase):
     get_source_files() function.
     """
 
+    @unittest.skipIf(os.environ.get("SKIP_LINTERS"), "requested via SKIP_LINTERS env variable")
     def test_flake8(self):
         """Test: Run flake8 on Python source code."""
         cmd = [sys.executable, "-m", "flake8", "--max-line-length=99"] + get_source_files()

tests/test_isort.py

@@ -14,6 +14,7 @@
 
 """Run isort to check if Python import definitions are sorted."""
 
+import os
 import subprocess
 import sys
 import unittest
@@ -28,6 +29,7 @@ class IsortTestCase(unittest.TestCase):
     is provided by the get_source_files() function.
     """
 
+    @unittest.skipIf(os.environ.get("SKIP_LINTERS"), "requested via SKIP_LINTERS env variable")
     def test_isort(self):
         """Test: Run isort on Python source code."""
 

tests/test_pylint.py

@@ -38,6 +38,8 @@ def test_pylint(self):
         """Test: Run pylint on Python source code."""
 
         cmd = [sys.executable, "-m", "pylint", "--rcfile=" + CONFIG, "--"] + get_source_files()
+        if os.environ.get("SKIP_LINTERS"):
+            cmd.insert(4, "--errors-only")
         if unittest_verbosity() >= 2:
             sys.stderr.write(f"Running following command:\n{' '.join(cmd)}\n")
         with subprocess.Popen(

tests/test_shellcheck.py

@@ -14,6 +14,7 @@
 
 """Run shellcheck on Shell code."""
 
+import os
 import subprocess
 import sys
 import unittest
@@ -29,6 +30,7 @@ class ShellcheckTestCase(unittest.TestCase):
     on Shell source code.
     """
 
+    @unittest.skipIf(os.environ.get("SKIP_LINTERS"), "requested via SKIP_LINTERS env variable")
     def test_shellcheck(self):
         """Test: Run shellcheck on Shell source code."""
         cmd = ["shellcheck"] + [get_path(s) for s in SHELL_SCRIPTS]