Write tests that let you simulate a user interacting with your Lamdera app.
In order for this package to work, all Cmds and Subs need to be replaced with Command and Subscription.
Additionally, the following modules
Browser.Dom
Browser.Events
Browser.Navigation
File
File.Download
File.Select
Http
Lamdera
Process
Task
Time
need to be replaced with
Effect.Browser.Dom
Effect.Browser.Events
Effect.Browser.Navigation
Effect.File
Effect.File.Download
Effect.File.Select
Effect.Http
Effect.Lamdera
Effect.Process
Effect.Task
Effect.Time
anywhere they are imported or used. A consequence of this is that you'll need to vendor any packages that use these modules in order to fix their imports.
To save time, you can automatically do this by running npx elm-review --template lamdera/program-test/upgrade --fix-all in the root folder of your Lamdera app.
You'll still need to fix some compiler errors afterwards but it should spare you most of the busywork.
Note that while the Effect.* version of these modules tries to match the API of the original module in most cases, sometimes that's not possible, and in a few places, they differ intentionally in order to provide a better user experience.
For example, Process.sleep takes a Float and you have to read the docs to know that's in milliseconds. Effect.Process.sleep instead uses Duration which lets you choose if you want to use milliseconds, seconds, minutes, etc.