Issue #18441: Make test.support.requires('gui') skip when it should.

(Consolidating this check and various checks in tkinter files and moving them
to test.support and test.regrtest will be another issue.)

Lib/idlelib/idle_test/test_text.py

@@ -216,10 +216,7 @@ class TkTextTest(TextTest, unittest.TestCase):
         requires('gui')
         from Tkinter import Tk, Text
         cls.Text = Text
-        try:
-            cls.root = Tk()
-        except TclError as msg:
-            raise unittest.SkipTest('TclError: %s' % msg)
+        cls.root = Tk()
 
     @classmethod
     def tearDownClass(cls):

Lib/test/test_idle.py

-# Skip test if _tkinter or _thread wasn't built or idlelib was deleted.
-from test.test_support import import_module
-import_module('Tkinter')
-import_module('threading')  # imported by PyShell, imports _thread
+# Skip test if _thread or _tkinter wasn't built or idlelib was deleted.
+from test.test_support import import_module, use_resources
+import_module('threading')  # imported by idlelib.PyShell, imports _thread
+tk = import_module('Tkinter')
 idletest = import_module('idlelib.idle_test')
 
+# If buildbot improperly sets gui resource (#18365, #18441), remove it
+# so requires('gui') tests are skipped while non-gui tests still run.
+if use_resources and 'gui' in use_resources:
+    try:
+        root = tk.Tk()
+        root.destroy()
+    except TclError:
+        while True:
+            use_resources.delete('gui')
+            if 'gui' not in use_resources:
+                break
+
 # Without test_main present, regrtest.runtest_inner (line1219) calls
 # unittest.TestLoader().loadTestsFromModule(this_module) which calls
 # load_tests() if it finds it. (Unittest.main does the same.)