This is a small demo of how to use the OpenFeature library to evaluate feature flags in your program, this example uses flagd as the provider in the main application (in cmd/main.go) but there are many other providers (see a list here for Go).
To run flagd I use this command:
docker run \
--rm -it \
--name flagd \
-p 8013:8013 \
-v .:/data \
ghcr.io/open-feature/flagd:latest start \
--uri file:///data/flags.flagd.jsonIt mounts the root directory into the container under /data, when the program is running you can edit the flags json file to change the "defaultVariant" to "on" or "off" and you should see the message printed out changes accordingly.
For a simple approach to unit testing there is a package called "github.com/open-feature/go-sdk/openfeature/memprovider" in the main library which provides and "InMemoryProvider", I set up the provider in the test and create a new client to pass to my code to test which lets us bypass using flagd for our unit testing purposes. Doing it this way makes our test cases more explicit as we have to set up the flags for each test-case.