diff --git a/starlette/routing.py b/starlette/routing.py
index 46f8b56285..8233f1cbe4 100644
--- a/starlette/routing.py
+++ b/starlette/routing.py
@@ -1,6 +1,6 @@
 import asyncio
-import inspect
 import functools
+import inspect
 import re
 import traceback
 import typing
@@ -29,11 +29,15 @@ class Match(Enum):
     FULL = 2
 
 
-def assert_args_is_only_route(func: typing.Callable) -> typing.Callable:
+def verify_args_is_only_route(func: typing.Callable) -> typing.Callable:
+    """Raise TypeError if number of positional arguments is not exactly 1."""
+
     @functools.wraps(func)
     def wrapper(self: BaseRoute, *args: str, **kwargs: str) -> URLPath:
-        assert len(args) > 0, "Missing route name as the first argument."
-        assert len(args) < 2, "Invalid positional argument passed."
+        if len(args) < 1:
+            raise TypeError("Missing route name as the first argument.")
+        if len(args) > 1:
+            raise TypeError("Invalid positional argument passed.")
         return func(self, *args, **kwargs)
 
     return wrapper
@@ -195,7 +199,7 @@ def matches(self, scope: Scope) -> typing.Tuple[Match, Scope]:
                     return Match.FULL, child_scope
         return Match.NONE, {}
 
-    @assert_args_is_only_route
+    @verify_args_is_only_route
     def url_path_for(self, *args: str, **kwargs: str) -> URLPath:
         seen_params = set(kwargs.keys())
         expected_params = set(self.param_convertors.keys())
@@ -259,7 +263,7 @@ def matches(self, scope: Scope) -> typing.Tuple[Match, Scope]:
                 return Match.FULL, child_scope
         return Match.NONE, {}
 
-    @assert_args_is_only_route
+    @verify_args_is_only_route
     def url_path_for(self, *args: str, **kwargs: str) -> URLPath:
         seen_params = set(kwargs.keys())
         expected_params = set(self.param_convertors.keys())
@@ -331,7 +335,7 @@ def matches(self, scope: Scope) -> typing.Tuple[Match, Scope]:
                 return Match.FULL, child_scope
         return Match.NONE, {}
 
-    @assert_args_is_only_route
+    @verify_args_is_only_route
     def url_path_for(self, *args: str, **kwargs: str) -> URLPath:
         name = args[0]
         if self.name is not None and name == self.name and "path" in kwargs:
@@ -400,7 +404,7 @@ def matches(self, scope: Scope) -> typing.Tuple[Match, Scope]:
                 return Match.FULL, child_scope
         return Match.NONE, {}
 
-    @assert_args_is_only_route
+    @verify_args_is_only_route
     def url_path_for(self, *args: str, **kwargs: str) -> URLPath:
         name = args[0]
         if self.name is not None and name == self.name and "path" in kwargs:
@@ -584,7 +588,7 @@ async def not_found(self, scope: Scope, receive: Receive, send: Send) -> None:
             response = PlainTextResponse("Not Found", status_code=404)
         await response(scope, receive, send)
 
-    @assert_args_is_only_route
+    @verify_args_is_only_route
     def url_path_for(self, *args: str, **kwargs: str) -> URLPath:
         for route in self.routes:
             try:
diff --git a/starlette/templating.py b/starlette/templating.py
index e63e98a983..a60ace5fb2 100644
--- a/starlette/templating.py
+++ b/starlette/templating.py
@@ -55,8 +55,10 @@ def __init__(self, directory: str) -> None:
     def get_env(self, directory: str) -> "jinja2.Environment":
         @jinja2.contextfunction
         def url_for(context: dict, *args: str, **kwargs: typing.Any) -> str:
-            assert len(args) > 0, "Missing route name as the first argument."
-            assert len(args) < 2, "Invalid positional argument passed."
+            if len(args) < 1:
+                raise TypeError("Missing route name as the second argument.")
+            if len(args) > 1:
+                raise TypeError("Invalid positional argument passed.")
             request = context["request"]
             return request.url_for(args[0], **kwargs)
 
diff --git a/tests/.ignore_lifespan b/tests/.ignore_lifespan
index 0a33582179..c517550bb8 100644
--- a/tests/.ignore_lifespan
+++ b/tests/.ignore_lifespan
@@ -1,3 +1,9 @@
 [coverage:run]
 omit =
   starlette/middleware/lifespan.py
+
+[report]
+exclude_lines =
+  pragma: no cover
+  pragma: nocover
+  raise NotImplementedError
diff --git a/tests/test_requests.py b/tests/test_requests.py
index 9713014d97..c1985c2a99 100644
--- a/tests/test_requests.py
+++ b/tests/test_requests.py
@@ -290,8 +290,8 @@ def test_request_url_for():
     app = Starlette()
 
     @app.route("/users/{name}")
-    async def func_users(request):  # pragma: no cover
-        ...
+    async def func_users(request):
+        raise NotImplementedError()  # ignored by coverage
 
     @app.route("/test")
     async def func_url_for_test(request: Request):
diff --git a/tests/test_routing.py b/tests/test_routing.py
index 0a358f21fc..0a4c6f6144 100644
--- a/tests/test_routing.py
+++ b/tests/test_routing.py
@@ -172,9 +172,9 @@ def test_url_path_for():
         app.url_path_for("user", username="tom/christie")
     with pytest.raises(AssertionError):
         app.url_path_for("user", username="")
-    with pytest.raises(AssertionError):
+    with pytest.raises(TypeError):
         assert app.url_path_for("user", "args2", name="tomchristie1")
-    with pytest.raises(AssertionError):
+    with pytest.raises(TypeError):
         assert app.url_path_for(name="tomchristie1")
 
 
diff --git a/tests/test_templates.py b/tests/test_templates.py
index a0ab3e1b0b..d5ecc1495f 100644
--- a/tests/test_templates.py
+++ b/tests/test_templates.py
@@ -15,6 +15,12 @@ def test_templates(tmpdir):
     app = Starlette(debug=True)
     templates = Jinja2Templates(directory=str(tmpdir))
 
+    url_for_func = templates.env.globals["url_for"]
+    with pytest.raises(TypeError):
+        assert url_for_func({}, "user", "args2", name="tomchristie")
+    with pytest.raises(TypeError):
+        assert url_for_func({}, name="tomchristie")
+
     @app.route("/")
     async def homepage(request):
         return templates.TemplateResponse("index.html", {"request": request})