Passby - 100% Elixir, 0-dependency mock HTTP server (Bypass drop-in replacement)

This is great! The only thing I’d additionally consider is maybe adding a convenience struct.url field:

- url = "http://127.0.0.1:#{bypass.port}/api/users/42"
- assert {:ok, %{"name" => "Alice"}} = MyClient.get_user(url)
+ assert {:ok, %{"name" => "Alice"}} = MyClient.get_user("#{bypass.url}/api/users/42")

or having a separate some kind of %{url: url} = Passby.start(). In any case, awesome idea with (essentially) zero dependency replacement!

Edit: oh, it truly has zero dependencies as you’re re-implementing most commonly used Plug API. That’s interesting!

Very good! I usually prefer to have a real server to test network-touching code. It’s a welcome addition to the ecosystem.

I’ve just added this in passby v0.1.1 while keeping 100% backward compatibility with Bypass:

Now %Passby{} includes the `.url` field, and there’s also a helper Passby.url/1,2:

# 1. Using the struct field:
assert {:ok, %{"name" => "Alice"}} = MyClient.get_user("#{bypass.url}/api/users/42")

# 2. Or using the Passby.url/2 helper (handles leading slashes automatically):
assert {:ok, %{"name" => "Alice"}} = MyClient.get_user(Passby.url(bypass, "/api/users/42"))

# 3. Existing Bypass-style code using .port continues to work unchanged:
assert {:ok, %{"name" => "Alice"}} = MyClient.get_user("http://127.0.0.1:#{bypass.port}/api/users/42")

Regarding the zero dependencies, yes, exactly! It relies entirely on standard Erlang/OTP (:gen_tcp, :inet, and :erlang.decode_packet) and provides a lightweight Passby.Conn struct matching Plug.Conn’s API conventions. This allows existing tests to migrate cleanly without bringing Cowboy, Ranch, or Plug into the dependency tree.

Thanks again for the input!

New passby v0.2.0, which ensures better compatibility with params (mainly path_params).