zorn
Phoenix’s built-in LiveView test helpers require you to hand-build the form payload and start a fresh pipe after every click. Worse, that payload means a test can pass even when the button it “submits” was renamed.
phoenix_test writes the entire flow as a single pipe from the user’s point of view and fails with a focused error instead of the entire page’s HTML. I used it on my last side project, and I don’t want to turn back.
Where Next?
Trending in Blog Posts
Other Trending Topics
Latest on Elixir Forum
Sponsor Spotlight
At WyeWorks, we believe great software is built by combining technical excellence with genuine human connection
Categories:
Sub Categories:
Forums
Popular Tags
- #ecto
- #liveview
- #troubleshooting
- #learning-elixir
- #library
- #deployment
- #erlang
- #testing
- #genserver
- #mix
- #absinthe
- #remote-other
- #otp
- #plug
- #how-to-question
- #macros
- #postgres
- #elixirconf
- #channels
- #exunit
- #discussion
- #code-sync
- #podcasts
- #javascript
- #onsite
- #dialyzer
- #docker
- #authentication
- #umbrella
- #ai
- #full-time-contract
- #podcasts-by-brainlid
- #ecto-query
- #blog-post
- #elixirconf-us
- #elixir-ls
- #phoenix_html
- #iex
- #graphql
- #genstage
- #websockets
- #supervisor
- #advent-of-code
- #distillery
- #processes
- #elixirconf-eu
- #api
- #forms
- #security
- #metaprogramming
Our Sponsors
Build Elixir applications with speed and confidence.
Supporting innovation across the BEAM ecosystem.
We build reliable cloud platforms for business-critical systems.
Catch errors, track performance, monitor hosts and more.
Elixir, Erlang & BEAM conferences from Code Sync - join us in 2026!
Master modern tools, write cleaner code, and tackle real-world challenges.
Bringing learning, work and compliance together since 1987.
The deployment platform built for Elixir: PaaS ease, VPS control.
The team behind Membrane, Popcorn, LiveDebugger. Available for hire.
Courses that'll move you from confusion to "Aha, now I get it!"
Showing Posts 1 to 6- Show Best Posts
- Show All (oldest first)
- Show All (newest first)
dimitarvp
I have used
phoenix_testand loved it but noticed a real added wall-clock time using it.zorn
I’ll have to keep an eye out for that and see if any performance increases should be considered. In general, I’m happy to give up some cycles for this kind of readability tradeoff. I wonder aloud if this is a larger
phoenix_testproject in the wild I should look to for a sample.dbaer
I hadn’t noticed, but I had migrated during major performance refactors to my tests (20 minutes to less than 30 seconds for the suite
). I’m surprised there is much difference between phoenix_test and not
zorn
I did some AI-sourced experiments on the performance question to scratch a personal curiosity.
The main finding (not verified personally) was that, yes, there is some slowdown when using
phoenix_test. It seems to range from 1.3 to 1.6 times slower on most things (and a larger 3.8x on form-submit flows), but mostly because it does more detailed work and runsrender(view)a lot more.The AI’s report suggested that if you are seeing slow test suite wall clocks, make sure you are reaching for
async: truebefore investing in other more drastic findings, which makes sense to me.https://github.com/zorn/phoenix_test/blob/wayfinder/perf-optimizations/bench/OPTIMIZATION-FINDINGS.md#phoenix_test-optimization-findings
In my LocalCents project, almost all my tests are
async: trueand when run on my M1 Max,mix testsruns 20 modules at a time. I think GitHub CI runs only about 8 at a time.dimitarvp
I think it was related to spawning a browser but that’s more than 12 months in the past now so can’t remember well. Thanks for following up.
hugobarauna
Agents are usually good at performance optimization.
Wondering if one could point their agent to it, ask it to optimize, and see what happens.
(yes, it’s a “lazy comment” expecting someone would do this
and report back)