Document Bash completion setup

docs/development.md

@@ -168,3 +168,17 @@ go run ./examples/core workspace greet --count=0 --tag=first --tag second
 
 The [consumer guide](consumers/guide.md) explains how their public API usage
 fits together.
+
+
+## Shell completion validation
+
+The opt-in interactive completion checks require Bash, Zsh, Fish, Python with
+`pexpect`, and the Bash completion package. The harness starts a clean Bash
+and sources `/usr/share/bash-completion/bash_completion` by default. Set
+`COMPLETION_BASH_INIT` to your installation's initialization file if it is
+elsewhere. See the [operator setup](cli.md#shell-completion) for ordinary use.
+
+```sh
+COMMANDKIT_COMPLETION_SHELLS=1 go test -count=1 -run '^TestCompletionShells$' ./internal/cobra
+COMMANDKIT_COMPLETION_SHELLS=1 go test -count=1 -run '^TestCompletionConsumerInShells$' .
+```