Add a --lint-only flag to the tests command.

Makefile

@@ -11,7 +11,7 @@ depends:
 
 .PHONY: lint
 lint:
-	$(PYTHON) -m flake8 --ignore E24,E121,E123,E125,E126,E221,E226,E266,E704,E265 --exclude ptvsd/pydevd $(CURDIR)
+	$(PYTHON) -m tests --lint-only
 
 .PHONY: test
 test:  ## Run the test suite.

tests/__main__.py

@@ -13,6 +13,7 @@ def convert_argv(argv):
     help  = False
     quick = False
     lint = False
+    runtests = True
     args = []
     modules = set()
     for arg in argv:
@@ -25,6 +26,10 @@ def convert_argv(argv):
         elif arg == '--lint':
             lint = True
             continue
+        elif arg == '--lint-only':
+            lint = True
+            runtests = False
+            continue
 
         # Unittest's main has only flags and positional args.
         # So we don't worry about options with values.
@@ -60,7 +65,7 @@ def convert_argv(argv):
             '--top-level-directory', PROJECT_ROOT,
             '--start-directory', start,
         ]
-    return cmd + args, lint
+    return cmd + args, runtests, lint
 
 
 def fix_sys_path():
@@ -88,8 +93,10 @@ def check_lint():
 
 
 if __name__ == '__main__':
-    argv, lint = convert_argv(sys.argv[1:])
+    argv, runtests, lint = convert_argv(sys.argv[1:])
     fix_sys_path()
     if lint:
         check_lint()
-    unittest.main(module=None, argv=argv)
+    if runtests:
+        print('running tests...')
+        unittest.main(module=None, argv=argv)