Fix functions_view.py (#1213)

### Motivation and Context
#1212 

### Description
Fixed a bug in the process of checking native function.


---------

Co-authored-by: Abby Harrison <54643756+awharrison-28@users.noreply.github.com>
Co-authored-by: Devis Lucato <dluc@users.noreply.github.com>

python/semantic_kernel/skill_definition/functions_view.py

@@ -43,4 +43,17 @@ def is_semantic(self, skill_name: str, function_name: str) -> bool:
         return as_sf
 
     def is_native(self, skill_name: str, function_name: str) -> bool:
-        return not self.is_semantic(skill_name, function_name)
+        as_sf = self._semantic_functions.get(skill_name, [])
+        as_sf = any(f.name == function_name for f in as_sf)
+
+        as_nf = self._native_functions.get(skill_name, [])
+        as_nf = any(f.name == function_name for f in as_nf)
+
+        if as_sf and as_nf:
+            raise KernelException(
+                KernelException.ErrorCodes.AmbiguousImplementation,
+                f"There are 2 functions with the same name: {function_name}."
+                f"One is native and the other semantic.",
+            )
+
+        return as_nf

python/tests/unit/skill_definition/test_functions_view.py

@@ -0,0 +1,152 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+import pytest
+from semantic_kernel.kernel_exception import KernelException
+from semantic_kernel.skill_definition.function_view import FunctionView
+from semantic_kernel.skill_definition.functions_view import FunctionsView, FunctionView
+
+
+def test_add_semantic_function():
+    view = FunctionView(
+        name="function1",
+        skill_name="skill1",
+        description="Semantic function",
+        parameters=[],
+        is_semantic=True,
+        is_asynchronous=True,
+    )
+    functions_view = FunctionsView()
+    functions_view.add_function(view)
+    semantic_functions = functions_view._semantic_functions.get("skill1")
+    assert len(semantic_functions) == 1
+    assert semantic_functions[0] == view
+
+
+def test_add_native_function():
+    view = FunctionView(
+        name="function2",
+        skill_name="skill2",
+        description="Native function",
+        parameters=[],
+        is_semantic=False,
+        is_asynchronous=True,
+    )
+    functions_view = FunctionsView()
+    functions_view.add_function(view)
+    native_functions = functions_view._native_functions.get("skill2")
+    assert len(native_functions) == 1
+    assert native_functions[0] == view
+
+
+def test_add_multiple_functions():
+    semantic_function = FunctionView(
+        name="function1",
+        skill_name="skill1",
+        description="Semantic function",
+        parameters=[],
+        is_semantic=True,
+        is_asynchronous=True,
+    )
+    native_function = FunctionView(
+        name="function2",
+        skill_name="skill2",
+        description="Native function",
+        parameters=[],
+        is_semantic=False,
+        is_asynchronous=True,
+    )
+    functions_view = FunctionsView()
+    functions_view.add_function(semantic_function)
+    functions_view.add_function(native_function)
+    semantic_functions = functions_view._semantic_functions.get("skill1")
+    native_functions = functions_view._native_functions.get("skill2")
+    assert len(semantic_functions) == 1
+    assert semantic_functions[0] == semantic_function
+    assert len(native_functions) == 1
+    assert native_functions[0] == native_function
+
+
+def test_is_semantic():
+    semantic_function = FunctionView(
+        name="function1",
+        skill_name="skill1",
+        description="Semantic function",
+        parameters=[],
+        is_semantic=True,
+        is_asynchronous=True,
+    )
+    native_function = FunctionView(
+        name="function2",
+        skill_name="skill2",
+        description="Native function",
+        parameters=[],
+        is_semantic=False,
+        is_asynchronous=True,
+    )
+    functions_view = FunctionsView()
+    functions_view.add_function(semantic_function)
+    functions_view.add_function(native_function)
+    assert functions_view.is_semantic("skill1", "function1") is True
+    assert functions_view.is_semantic("skill2", "function2") is False
+    assert functions_view.is_semantic("skill1", "unregistered_function") is False
+
+
+def test_is_native():
+    semantic_function = FunctionView(
+        name="function1",
+        skill_name="skill1",
+        description="Semantic function",
+        parameters=[],
+        is_semantic=True,
+        is_asynchronous=True,
+    )
+    native_function = FunctionView(
+        name="function2",
+        skill_name="skill2",
+        description="Native function",
+        parameters=[],
+        is_semantic=False,
+        is_asynchronous=True,
+    )
+    functions_view = FunctionsView()
+    functions_view.add_function(semantic_function)
+    functions_view.add_function(native_function)
+    assert functions_view.is_native("skill1", "function1") is False
+    assert functions_view.is_native("skill2", "function2") is True
+    assert functions_view.is_native("skill2", "unregistered_function") is False
+
+
+def test_ambiguous_implementation():
+    semantic_function = FunctionView(
+        name="function1",
+        skill_name="skill1",
+        description="Semantic function",
+        parameters=[],
+        is_semantic=True,
+        is_asynchronous=True,
+    )
+    native_function = FunctionView(
+        name="function1",
+        skill_name="skill1",
+        description="Native function",
+        parameters=[],
+        is_semantic=False,
+        is_asynchronous=True,
+    )
+    functions_view = FunctionsView()
+    functions_view.add_function(semantic_function)
+    functions_view.add_function(native_function)
+
+    with pytest.raises(KernelException) as exc_info:
+        functions_view.is_semantic("skill1", "function1")
+
+    assert (
+        exc_info.value.error_code == KernelException.ErrorCodes.AmbiguousImplementation
+    )
+
+    with pytest.raises(KernelException) as exc_info:
+        functions_view.is_native("skill1", "function1")
+
+    assert (
+        exc_info.value.error_code == KernelException.ErrorCodes.AmbiguousImplementation
+    )