Fix typo in testing_controllers.md (#2970)

I believe there should be a period instead of slash.

guides/testing/testing_controllers.md

@@ -150,7 +150,7 @@ defmodule HelloWeb.UserControllerTest do
   end
 ```
 
-Let's take a look at what's going on here. First we alias `Hello.Accounts`, the context module that provides us with our repository manipulation functions. When we use the `HelloWeb.ConnCase` module, it sets things up such that each connection is wrapped in a transaction, *and* all of the database interactions inside of the test use the same database connection and transaction. This module also sets up a `conn` attribute in our ExUnit context, using `Phoenix.ConnCase/build_conn/0`. We then pattern match this to use it in each test case. For details, take a look at the file `test/support/conn_case.ex`, as well as the [Ecto documentation for SQL.Sandbox](https://hexdocs.pm/ecto/Ecto.Adapters.SQL.Sandbox.html). We could put a `build_conn/0` call inside of each test, but it is cleaner to use a setup block to do it.
+Let's take a look at what's going on here. First we alias `Hello.Accounts`, the context module that provides us with our repository manipulation functions. When we use the `HelloWeb.ConnCase` module, it sets things up such that each connection is wrapped in a transaction, *and* all of the database interactions inside of the test use the same database connection and transaction. This module also sets up a `conn` attribute in our ExUnit context, using `Phoenix.ConnCase.build_conn/0`. We then pattern match this to use it in each test case. For details, take a look at the file `test/support/conn_case.ex`, as well as the [Ecto documentation for SQL.Sandbox](https://hexdocs.pm/ecto/Ecto.Adapters.SQL.Sandbox.html). We could put a `build_conn/0` call inside of each test, but it is cleaner to use a setup block to do it.
 
 The index test then hooks into the context to extract the contents of the `:conn` key. We then create two users using the `Hello.Accounts.create_user/1` function. Again, note that this function accesses the test repo, but even though we don't pass the `conn` variable to the call, it still uses the same connection and puts these new users inside the same database transaction. Next the `conn` is piped to a `get` function to make a `GET` request to our `UserController` index action, which is in turn piped into `json_response/2` along with the expected HTTP status code. This will return the JSON from the response body, when everything is wired up properly. We represent the JSON we want the controller action to return with the variable `expected`, and assert that the `response` and `expected` are the same.