test hookcaller: targeted testing for multi impl scenario

Author: wahuneke

testing/test_hookcaller.py

@@ -511,3 +511,56 @@ def extra2() -> str:
         "2",
         "3",
     ]
+
+
+def test_hook_multi_impl(pm: PluginManager) -> None:
+    """A plugin can implement the same spec multiple times
+    via specname= on hookimpl."""
+
+    class Api:
+        @hookspec
+        def hello(self, arg: object) -> None:
+            "api hook 1"
+
+    pm.add_hookspecs(Api)
+    hook = pm.hook
+    test_hc = hook.hello
+
+    class Plugin:
+        @hookimpl
+        def hello(self, arg):
+            return arg + 1
+
+        @hookimpl(specname="hello")
+        def hello_again(self, arg):
+            return arg + 100
+
+    plugin = Plugin()
+
+    pm.register(plugin)
+    out = test_hc(arg=3)
+    assert out == [103, 4]
+
+    assert len(pm.get_plugins()) == 1
+
+    hookimpls = test_hc.get_hookimpls()
+    hook_plugins = [item.plugin for item in hookimpls]
+    assert hook_plugins == [plugin, plugin]
+    for impl in hookimpls:
+        pm._verify_hook(test_hc, impl)
+
+    hook_callers = pm.get_hookcallers(plugin)
+    assert hook_callers is not None
+    assert len(hook_callers) == 1
+    assert hook_callers[0] is test_hc
+
+    subset_caller = pm.subset_hook_caller("hello", [plugin])
+    out = subset_caller(arg=3)
+    assert out == []
+
+    pm.unregister(plugin)
+    assert test_hc(arg=3) == []
+    hookimpls = test_hc.get_hookimpls()
+    assert hookimpls == []
+    hook_callers = pm.get_hookcallers(plugin)
+    assert hook_callers is None