Add has_plugin method to PluginManager

Author: nicoddemus

pluggy.py

@@ -456,6 +456,10 @@ def get_plugin(self, name):
         """ Return a plugin or None for the given name. """
         return self._name2plugin.get(name)
 
+    def has_plugin(self, name):
+        """ Return True if a plugin with the given name is registered. """
+        return self.get_plugin(name) is not None
+
     def get_name(self, plugin):
         """ Return name for registered plugin or None if not registered. """
         for name, val in self._name2plugin.items():

testing/test_pluggy.py

@@ -56,6 +56,15 @@ class A:
         assert len(l) == 1
         assert l == [("hello", a2)]
 
+    def test_has_plugin(self, pm):
+        class A:
+            pass
+
+        a1 = A()
+        pm.register(a1, 'hello')
+        assert pm.is_registered(a1)
+        assert pm.has_plugin('hello')
+
     def test_register_dynamic_attr(self, he_pm):
         class A:
             def __getattr__(self, name):