How to test an opam feature

From a tagged release (including pre-releases)

If the binary is present in the releases page, it can be installed using the install.sh script. If your opam root is not in the usual location ~/.opam, set the OPAMROOT environment variable before calling it.

sh <(curl -sL https://raw.githubusercontent.com/ocaml/opam/master/shell/install.sh) --dev --backup

To test a release other than the latest, change master to the tag name.

Cleaning

The install script can restore the opam binary and root from a backup. The previous version was given on the previous command, which can be found in the backup directory of the form <opamroot>.<version>.

sh <(curl -sL https://raw.githubusercontent.com/ocaml/opam/master/shell/install.sh) --restore <version>

From sources

You can use your current opam binary. In order not to swamp your current switches, we will create a new one, install opam, and do a backup of your opam root.

$ opam sw cr test_opam --empty # or choose your preferred compiler
$ eval $(opam env)
$ opam pin git+https://github.com/ocaml/opam
$ cp <opamroot>/lib/opam-devel/opam <prefix>
$ chmod +x <prefix>/opam
$ cp -R <opamroot> <opamroot>.backup

If you don't want to use you current installed opam root, you can follow opam-devel's post-install message and make an alias with a fresh opam root.

$ alias opam2="OPAMROOT=~/.opam2 <opamroot>/lib/opam-devel/opam"

From a PR

As for building from sources, but you need to pin the pull request branch.

$ opam pin git+https://github.com/ocaml/opam#pull/<PR_ID>/head

Cleaning

If your new opam root is no longer needed, you can recover the backup, and remove the newly created switch.

$ rm -r <opamroot>
$ cp -r <opamroot>.backup <opamroot>
$ opam switch remove test_opam