gh-71339: Add additional assertion methods for unittest (GH-128707)

Add the following methods:

* assertHasAttr() and assertNotHasAttr()
* assertIsSubclass() and assertNotIsSubclass()
* assertStartsWith() and assertNotStartsWith()
* assertEndsWith() and assertNotEndsWith()

Also improve error messages for assertIsInstance() and
assertNotIsInstance().

Lib/unittest/case.py

@@ -1321,13 +1321,67 @@ class TestCase(object):
         """Same as self.assertTrue(isinstance(obj, cls)), with a nicer
         default message."""
         if not isinstance(obj, cls):
-            standardMsg = '%s is not an instance of %r' % (safe_repr(obj), cls)
+            if isinstance(cls, tuple):
+                standardMsg = f'{safe_repr(obj)} is not an instance of any of {cls!r}'
+            else:
+                standardMsg = f'{safe_repr(obj)} is not an instance of {cls!r}'
             self.fail(self._formatMessage(msg, standardMsg))
 
     def assertNotIsInstance(self, obj, cls, msg=None):
         """Included for symmetry with assertIsInstance."""
         if isinstance(obj, cls):
-            standardMsg = '%s is an instance of %r' % (safe_repr(obj), cls)
+            if isinstance(cls, tuple):
+                for x in cls:
+                    if isinstance(obj, x):
+                        cls = x
+                        break
+            standardMsg = f'{safe_repr(obj)} is an instance of {cls!r}'
+            self.fail(self._formatMessage(msg, standardMsg))
+
+    def assertIsSubclass(self, cls, superclass, msg=None):
+        try:
+            if issubclass(cls, superclass):
+                return
+        except TypeError:
+            if not isinstance(cls, type):
+                self.fail(self._formatMessage(msg, f'{cls!r} is not a class'))
+            raise
+        if isinstance(superclass, tuple):
+            standardMsg = f'{cls!r} is not a subclass of any of {superclass!r}'
+        else:
+            standardMsg = f'{cls!r} is not a subclass of {superclass!r}'
+        self.fail(self._formatMessage(msg, standardMsg))
+
+    def assertNotIsSubclass(self, cls, superclass, msg=None):
+        try:
+            if not issubclass(cls, superclass):
+                return
+        except TypeError:
+            if not isinstance(cls, type):
+                self.fail(self._formatMessage(msg, f'{cls!r} is not a class'))
+            raise
+        if isinstance(superclass, tuple):
+            for x in superclass:
+                if issubclass(cls, x):
+                    superclass = x
+                    break
+        standardMsg = f'{cls!r} is a subclass of {superclass!r}'
+        self.fail(self._formatMessage(msg, standardMsg))
+
+    def assertHasAttr(self, obj, name, msg=None):
+        if not hasattr(obj, name):
+            if isinstance(obj, types.ModuleType):
+                standardMsg = f'module {obj.__name__!r} has no attribute {name!r}'
+            else:
+                standardMsg = f'{type(obj).__name__} instance has no attribute {name!r}'
+            self.fail(self._formatMessage(msg, standardMsg))
+
+    def assertNotHasAttr(self, obj, name, msg=None):
+        if hasattr(obj, name):
+            if isinstance(obj, types.ModuleType):
+                standardMsg = f'module {obj.__name__!r} has unexpected attribute {name!r}'
+            else:
+                standardMsg = f'{type(obj).__name__} instance has unexpected attribute {name!r}'
             self.fail(self._formatMessage(msg, standardMsg))
 
     def assertRaisesRegex(self, expected_exception, expected_regex,
@@ -1391,6 +1445,80 @@ class TestCase(object):
             msg = self._formatMessage(msg, standardMsg)
             raise self.failureException(msg)
 
+    def _tail_type_check(self, s, tails, msg):
+        if not isinstance(tails, tuple):
+            tails = (tails,)
+        for tail in tails:
+            if isinstance(tail, str):
+                if not isinstance(s, str):
+                    self.fail(self._formatMessage(msg,
+                            f'Expected str, not {type(s).__name__}'))
+            elif isinstance(tail, (bytes, bytearray)):
+                if not isinstance(s, (bytes, bytearray)):
+                    self.fail(self._formatMessage(msg,
+                            f'Expected bytes, not {type(s).__name__}'))
+
+    def assertStartsWith(self, s, prefix, msg=None):
+        try:
+            if s.startswith(prefix):
+                return
+        except (AttributeError, TypeError):
+            self._tail_type_check(s, prefix, msg)
+            raise
+        a = safe_repr(s, short=True)
+        b = safe_repr(prefix)
+        if isinstance(prefix, tuple):
+            standardMsg = f"{a} doesn't start with any of {b}"
+        else:
+            standardMsg = f"{a} doesn't start with {b}"
+        self.fail(self._formatMessage(msg, standardMsg))
+
+    def assertNotStartsWith(self, s, prefix, msg=None):
+        try:
+            if not s.startswith(prefix):
+                return
+        except (AttributeError, TypeError):
+            self._tail_type_check(s, prefix, msg)
+            raise
+        if isinstance(prefix, tuple):
+            for x in prefix:
+                if s.startswith(x):
+                    prefix = x
+                    break
+        a = safe_repr(s, short=True)
+        b = safe_repr(prefix)
+        self.fail(self._formatMessage(msg, f"{a} starts with {b}"))
+
+    def assertEndsWith(self, s, suffix, msg=None):
+        try:
+            if s.endswith(suffix):
+                return
+        except (AttributeError, TypeError):
+            self._tail_type_check(s, suffix, msg)
+            raise
+        a = safe_repr(s, short=True)
+        b = safe_repr(suffix)
+        if isinstance(suffix, tuple):
+            standardMsg = f"{a} doesn't end with any of {b}"
+        else:
+            standardMsg = f"{a} doesn't end with {b}"
+        self.fail(self._formatMessage(msg, standardMsg))
+
+    def assertNotEndsWith(self, s, suffix, msg=None):
+        try:
+            if not s.endswith(suffix):
+                return
+        except (AttributeError, TypeError):
+            self._tail_type_check(s, suffix, msg)
+            raise
+        if isinstance(suffix, tuple):
+            for x in suffix:
+                if s.endswith(x):
+                    suffix = x
+                    break
+        a = safe_repr(s, short=True)
+        b = safe_repr(suffix)
+        self.fail(self._formatMessage(msg, f"{a} ends with {b}"))
 
 
 class FunctionTestCase(TestCase):