diff --git a/Lib/idlelib/calltip.py b/Lib/idlelib/calltip.py
index b013a7f..a3dda26 100644
--- a/Lib/idlelib/calltip.py
+++ b/Lib/idlelib/calltip.py
@@ -118,7 +118,7 @@
 _first_param = re.compile(r'(?<=\()\w*\,?\s*')
 _default_callable_argspec = "See source or doc"
 _invalid_method = "invalid method signature"
-_argument_positional = "\n['/' marks preceding arguments as positional-only]\n"
+_argument_positional = "  # '/' marks preceding args as positional-only."
 
 def get_argspec(ob):
     '''Return a string describing the signature of a callable object, or ''.
@@ -144,11 +144,11 @@
         if msg.startswith(_invalid_method):
             return _invalid_method
 
-    if '/' in argspec:
-        """Using AC's positional argument should add the explain"""
+    if '/' in argspec and len(argspec) < _MAX_COLS - len(_argument_positional):
+        # Add explanation TODO remove after 3.7, before 3.9.
         argspec += _argument_positional
     if isinstance(fob, type) and argspec == '()':
-        """fob with no argument, use default callable argspec"""
+        # If fob has no argument, use default callable argspec.
         argspec = _default_callable_argspec
 
     lines = (textwrap.wrap(argspec, _MAX_COLS, subsequent_indent=_INDENT)
diff --git a/Lib/idlelib/idle_test/test_calltip.py b/Lib/idlelib/idle_test/test_calltip.py
index 833351b..886959b 100644
--- a/Lib/idlelib/idle_test/test_calltip.py
+++ b/Lib/idlelib/idle_test/test_calltip.py
@@ -4,8 +4,7 @@
 import unittest
 import textwrap
 import types
-
-default_tip = calltip._default_callable_argspec
+import re
 
 
 # Test Class TC is used in multiple get_argspec test methods
@@ -28,6 +27,7 @@
     t6.tip = "(no, self)"
     def __call__(self, ci): 'doc'
     __call__.tip = "(self, ci)"
+    def nd(self): pass  # No doc.
     # attaching .tip to wrapped methods does not work
     @classmethod
     def cm(cls, a): 'doc'
@@ -36,11 +36,12 @@
 
 
 tc = TC()
-signature = calltip.get_argspec  # 2.7 and 3.x use different functions
+default_tip = calltip._default_callable_argspec
+get_spec = calltip.get_argspec
 
 
-class Get_signatureTest(unittest.TestCase):
-    # The signature function must return a string, even if blank.
+class Get_argspecTest(unittest.TestCase):
+    # The get_spec function must return a string, even if blank.
     # Test a variety of objects to be sure that none cause it to raise
     # (quite aside from getting as correct an answer as possible).
     # The tests of builtins may break if inspect or the docstrings change,
@@ -49,57 +50,59 @@
 
     def test_builtins(self):
 
+        def tiptest(obj, out):
+            self.assertEqual(get_spec(obj), out)
+
         # Python class that inherits builtin methods
         class List(list): "List() doc"
 
         # Simulate builtin with no docstring for default tip test
         class SB:  __call__ = None
 
-        def gtest(obj, out):
-            self.assertEqual(signature(obj), out)
-
         if List.__doc__ is not None:
-            gtest(List, '(iterable=(), /)' + calltip._argument_positional
-                  + '\n' + List.__doc__)
-        gtest(list.__new__,
+            tiptest(List,
+                    f'(iterable=(), /){calltip._argument_positional}'
+                    f'\n{List.__doc__}')
+        tiptest(list.__new__,
               '(*args, **kwargs)\n'
               'Create and return a new object.  '
               'See help(type) for accurate signature.')
-        gtest(list.__init__,
+        tiptest(list.__init__,
               '(self, /, *args, **kwargs)'
               + calltip._argument_positional + '\n' +
               'Initialize self.  See help(type(self)) for accurate signature.')
         append_doc = (calltip._argument_positional
                       + "\nAppend object to the end of the list.")
-        gtest(list.append, '(self, object, /)' + append_doc)
-        gtest(List.append, '(self, object, /)' + append_doc)
-        gtest([].append, '(object, /)' + append_doc)
+        tiptest(list.append, '(self, object, /)' + append_doc)
+        tiptest(List.append, '(self, object, /)' + append_doc)
+        tiptest([].append, '(object, /)' + append_doc)
 
-        gtest(types.MethodType, "method(function, instance)")
-        gtest(SB(), default_tip)
-        import re
+        tiptest(types.MethodType, "method(function, instance)")
+        tiptest(SB(), default_tip)
+
         p = re.compile('')
-        gtest(re.sub, '''\
+        tiptest(re.sub, '''\
 (pattern, repl, string, count=0, flags=0)
 Return the string obtained by replacing the leftmost
 non-overlapping occurrences of the pattern in string by the
 replacement repl.  repl can be either a string or a callable;
 if a string, backslash escapes in it are processed.  If it is
 a callable, it's passed the Match object and must return''')
-        gtest(p.sub, '''\
+        tiptest(p.sub, '''\
 (repl, string, count=0)
 Return the string obtained by replacing the leftmost \
 non-overlapping occurrences o...''')
 
     def test_signature_wrap(self):
         if textwrap.TextWrapper.__doc__ is not None:
-            self.assertEqual(signature(textwrap.TextWrapper), '''\
+            self.assertEqual(get_spec(textwrap.TextWrapper), '''\
 (width=70, initial_indent='', subsequent_indent='', expand_tabs=True,
     replace_whitespace=True, fix_sentence_endings=False, break_long_words=True,
     drop_whitespace=True, break_on_hyphens=True, tabsize=8, *, max_lines=None,
     placeholder=' [...]')''')
 
     def test_properly_formated(self):
+
         def foo(s='a'*100):
             pass
 
@@ -112,35 +115,35 @@
 
         indent = calltip._INDENT
 
-        str_foo = "(s='aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"\
-                  "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n" + indent + "aaaaaaaaa"\
-                  "aaaaaaaaaa')"
-        str_bar = "(s='aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"\
-                  "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n" + indent + "aaaaaaaaa"\
-                  "aaaaaaaaaa')\nHello Guido"
-        str_baz = "(s='aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"\
-                  "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n" + indent + "aaaaaaaaa"\
-                  "aaaaaaaaaa', z='bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"\
-                  "bbbbbbbbbbbbbbbbb\n" + indent + "bbbbbbbbbbbbbbbbbbbbbb"\
-                  "bbbbbbbbbbbbbbbbbbbbbb')"
+        sfoo = "(s='aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"\
+               "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n" + indent + "aaaaaaaaa"\
+               "aaaaaaaaaa')"
+        sbar = "(s='aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"\
+               "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n" + indent + "aaaaaaaaa"\
+               "aaaaaaaaaa')\nHello Guido"
+        sbaz = "(s='aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"\
+               "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n" + indent + "aaaaaaaaa"\
+               "aaaaaaaaaa', z='bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"\
+               "bbbbbbbbbbbbbbbbb\n" + indent + "bbbbbbbbbbbbbbbbbbbbbb"\
+               "bbbbbbbbbbbbbbbbbbbbbb')"
 
-        self.assertEqual(calltip.get_argspec(foo), str_foo)
-        self.assertEqual(calltip.get_argspec(bar), str_bar)
-        self.assertEqual(calltip.get_argspec(baz), str_baz)
+        for func,doc in [(foo, sfoo), (bar, sbar), (baz, sbaz)]:
+            with self.subTest(func=func, doc=doc):
+                self.assertEqual(get_spec(func), doc)
 
     def test_docline_truncation(self):
         def f(): pass
         f.__doc__ = 'a'*300
-        self.assertEqual(signature(f), '()\n' + 'a' * (calltip._MAX_COLS-3) + '...')
+        self.assertEqual(get_spec(f), f"()\n{'a'*(calltip._MAX_COLS-3) + '...'}")
 
     def test_multiline_docstring(self):
         # Test fewer lines than max.
-        self.assertEqual(signature(range),
+        self.assertEqual(get_spec(range),
                 "range(stop) -> range object\n"
                 "range(start, stop[, step]) -> range object")
 
         # Test max lines
-        self.assertEqual(signature(bytes), '''\
+        self.assertEqual(get_spec(bytes), '''\
 bytes(iterable_of_ints) -> bytes
 bytes(string, encoding[, errors]) -> bytes
 bytes(bytes_or_buffer) -> immutable copy of bytes_or_buffer
@@ -150,7 +153,7 @@
         # Test more than max lines
         def f(): pass
         f.__doc__ = 'a\n' * 15
-        self.assertEqual(signature(f), '()' + '\na' * calltip._MAX_LINES)
+        self.assertEqual(get_spec(f), '()' + '\na' * calltip._MAX_LINES)
 
     def test_functions(self):
         def t1(): 'doc'
@@ -166,14 +169,16 @@
 
         doc = '\ndoc' if t1.__doc__ is not None else ''
         for func in (t1, t2, t3, t4, t5, TC):
-            self.assertEqual(signature(func), func.tip + doc)
+            with self.subTest(func=func):
+                self.assertEqual(get_spec(func), func.tip + doc)
 
     def test_methods(self):
         doc = '\ndoc' if TC.__doc__ is not None else ''
         for meth in (TC.t1, TC.t2, TC.t3, TC.t4, TC.t5, TC.t6, TC.__call__):
-            self.assertEqual(signature(meth), meth.tip + doc)
-        self.assertEqual(signature(TC.cm), "(a)" + doc)
-        self.assertEqual(signature(TC.sm), "(b)" + doc)
+            with self.subTest(meth=meth):
+                self.assertEqual(get_spec(meth), meth.tip + doc)
+        self.assertEqual(get_spec(TC.cm), "(a)" + doc)
+        self.assertEqual(get_spec(TC.sm), "(b)" + doc)
 
     def test_bound_methods(self):
         # test that first parameter is correctly removed from argspec
@@ -181,7 +186,8 @@
         for meth, mtip  in ((tc.t1, "()"), (tc.t4, "(*args)"),
                             (tc.t6, "(self)"), (tc.__call__, '(ci)'),
                             (tc, '(ci)'), (TC.cm, "(a)"),):
-            self.assertEqual(signature(meth), mtip + doc)
+            with self.subTest(meth=meth, mtip=mtip):
+                self.assertEqual(get_spec(meth), mtip + doc)
 
     def test_starred_parameter(self):
         # test that starred first parameter is *not* removed from argspec
@@ -189,17 +195,18 @@
             def m1(*args): pass
         c = C()
         for meth, mtip  in ((C.m1, '(*args)'), (c.m1, "(*args)"),):
-            self.assertEqual(signature(meth), mtip)
+            with self.subTest(meth=meth, mtip=mtip):
+                self.assertEqual(get_spec(meth), mtip)
 
-    def test_invalid_method_signature(self):
+    def test_invalid_method_get_spec(self):
         class C:
             def m2(**kwargs): pass
         class Test:
             def __call__(*, a): pass
 
         mtip = calltip._invalid_method
-        self.assertEqual(signature(C().m2), mtip)
-        self.assertEqual(signature(Test()), mtip)
+        self.assertEqual(get_spec(C().m2), mtip)
+        self.assertEqual(get_spec(Test()), mtip)
 
     def test_non_ascii_name(self):
         # test that re works to delete a first parameter name that
@@ -208,12 +215,9 @@
         assert calltip._first_param.sub('', uni) == '(a)'
 
     def test_no_docstring(self):
-        def nd(s):
-            pass
-        TC.nd = nd
-        self.assertEqual(signature(nd), "(s)")
-        self.assertEqual(signature(TC.nd), "(s)")
-        self.assertEqual(signature(tc.nd), "()")
+        for meth, mtip in ((TC.nd, "(self)"), (tc.nd, "()")):
+            with self.subTest(meth=meth, mtip=mtip):
+                self.assertEqual(get_spec(meth), mtip)
 
     def test_attribute_exception(self):
         class NoCall:
@@ -229,11 +233,13 @@
         for meth, mtip  in ((NoCall, default_tip), (CallA, default_tip),
                             (NoCall(), ''), (CallA(), '(a, b, c)'),
                             (CallB(), '(ci)')):
-            self.assertEqual(signature(meth), mtip)
+            with self.subTest(meth=meth, mtip=mtip):
+                self.assertEqual(get_spec(meth), mtip)
 
     def test_non_callables(self):
         for obj in (0, 0.0, '0', b'0', [], {}):
-            self.assertEqual(signature(obj), '')
+            with self.subTest(obj=obj):
+                self.assertEqual(get_spec(obj), '')
 
 
 class Get_entityTest(unittest.TestCase):