feat: Adding ability to invoke functions directly (Azure#238)

* Adding new direct calling tests

* Adding comments and improving tests

azure/functions/decorators/function_app.py

@@ -75,6 +75,26 @@ def __init__(self, func: Callable[..., Any], script_file: str):
         self.http_type = 'function'
         self._is_http_function = False
 
+    def __str__(self):
+        """Return the function.json representation of the function"""
+        return self.get_function_json()
+
+    def __call__(self, *args, **kwargs):
+        """This would allow the Function object to be directly callable and runnable
+        directly using the interpreter locally.
+
+        Example:
+        @app.route(route="http_trigger")
+        def http_trigger(req: func.HttpRequest) -> func.HttpResponse:
+            return "Hello, World!"
+
+        print(http_trigger(None))
+
+        ➜ python function_app.py
+        Hello, World!
+        """
+        return self._func(*args, **kwargs)
+
     def add_binding(self, binding: Binding) -> None:
         """Add a binding instance to the function.
 
@@ -201,17 +221,15 @@ def get_function_json(self) -> str:
         """
         return json.dumps(self.get_dict_repr(), cls=StringifyEnumJsonEncoder)
 
-    def __str__(self):
-        return self.get_function_json()
-
 
 class FunctionBuilder(object):
 
     def __init__(self, func, function_script_file):
         self._function = Function(func, function_script_file)
 
     def __call__(self, *args, **kwargs):
-        pass
+        """Call the Function object directly"""
+        return self._function(*args, **kwargs)
 
     def configure_http_type(self, http_type: str) -> 'FunctionBuilder':
         self._function.set_http_type(http_type)

tests/decorators/test_function_app.py

@@ -543,6 +543,22 @@ def test_blueprint_same_function_and_method_name(name: str):
             " Please change @app.function_name() or the function"
             " method name to be unique.")
 
+    def test_user_function_is_directly_callable_no_args(self):
+        def test_validate_function_working_no_args():
+            return "dummy"
+
+        self.dummy = test_validate_function_working_no_args
+        self.fb = FunctionBuilder(self.dummy, "dummy.py")
+        self.assertEqual(self.fb(), "dummy")
+
+    def test_user_function_is_directly_callable_args(self):
+        def test_validate_function_working_sum_args(arg1: int, arg2: int):
+            return arg1 + arg2
+
+        self.dummy = test_validate_function_working_sum_args
+        self.fb = FunctionBuilder(self.dummy, "dummy.py")
+        self.assertEqual(self.fb(1, 2), 3)
+
 
 class TestScaffold(unittest.TestCase):
     def setUp(self):