symbolboxer
From Ruby to Elixir: Broken test for MessageController (182)
Hi! I believe I’ve found an erratum.
tl;dr: MessageController/create does not add changeset validation errors to the flash, which breaks one of its tests.
On page 182 we write this test:
test "invalid params is rejected", %{conn: conn} do
conn = post(conn, ~p"/messages/new", %{}) assert html_response(conn, 200) =~
Plug.HTML.html_escape("can't be blank")
end
Which resulted in this error when I ran it:
1) test POST /messages/new invalid params is rejected (PhoneAppWeb.MessageControllerTest)
test/phone_app_web/controllers/message_controller_test.exs:34
Assertion with =~ failed
code: assert html_response(conn, 200) =~ Plug.HTML.html_escape("can't be blank")
left: "<!DOCTYPE html>\n<html lang=\"en\" class=\"[scrollbar-gutter:stable]\">\n <head>
[rest of page truncated]
right: "can't be blank"
After some valuable Elixir debugging practice, I believe I have the cause. The test in this case is looking for a “can’t be blank” error somewhere on the page. In MessageController/create, there is code that takes errors and puts them into the flash on line 48. However, that code is never reached because changeset validation happens on line 43 and the error shoots us down to line 55. That error handler doesn’t do anything specifically with the error. It passes the changeset to the view to render, but I don’t see where in the view it would display the error. Thus, the validation error doesn’t appear on the rendered view, and the test can’t find it.
Thanks, and just let me know if I’ve gotten something wrong.
Marked As Solved
sb8244
Thanks for sharing that. I took a look at CoreComponents.input and found the definition was slightly varied. I changed this line:
# used to be:
# errors = if Phoenix.Component.used_input?(field), do: field.errors, else: []
errors = field.errors
and the test passes. This was a change in the latest implementation of CoreComponents, hence the difference.
Now, to get this test passing without modifying the above line, I had to tweak the test to pass in blank inputs:
test "invalid params is rejected", %{conn: conn} do
params = %{message: %{to: "", body: ""}}
conn = post(conn, ~p"/messages/new", params)
assert html_response(conn, 200) =~
Plug.HTML.html_escape("can't be blank")
end
We can look through the implementation of used_input? to see why this works. By passing in the data, the form.params field contains the input field, so it counts as “used”
Popular Pragmatic Bookshelf topics
Modern front-end development for Rails, second edition - Struggling to get the first chapter to work
Other popular topics
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /wasm
- /ruby
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /clojure
- /java
- /emacs
- /haskell
- /svelte
- /onivim
- /typescript
- /kotlin
- /c-plus-plus
- /crystal
- /tailwind
- /react
- /gleam
- /ocaml
- /elm
- /flutter
- /vscode
- /ash
- /html
- /opensuse
- /zig
- /deepseek
- /centos
- /php
- /scala
- /react-native
- /lisp
- /textmate
- /sublime-text
- /nixos
- /debian
- /agda
- /django
- /deno
- /kubuntu
- /arch-linux
- /nodejs
- /revery
- /ubuntu
- /spring
- /manjaro
- /lua
- /diversity
- /julia
- /markdown
- /v
Devtalk Sponsors
Practical resources that improve the lives of professional developers.
We build trusted fault-tolerant systems that scale to billions of users.
Real-time error tracking, performance insights, and observability for devs.
Supporting innovation across the BEAM ecosystem.
We build reliable cloud platforms for business-critical systems.
Develop your skills with books, videos, and courses.
Catch errors, track performance, monitor hosts and more.
Enabling companies to succeed by building software people love.
Courses that move you from confusion to "Aha, now I get it!"
Publishing Linux Magazine, ADMIN, and MakerSpace for 25+ years.