add e2e fish test

scripts/run-full-tests

@@ -18,7 +18,7 @@ if [ -z "$TEST_CONTAINER" ] ; then
 fi
 
 apk add --no-cache python3 py3-pip borgbackup postgresql-client mariadb-client mongodb-tools \
-    py3-ruamel.yaml py3-ruamel.yaml.clib bash sqlite
+    py3-ruamel.yaml py3-ruamel.yaml.clib bash sqlite fish
 # If certain dependencies of black are available in this version of Alpine, install them.
 apk add --no-cache py3-typed-ast py3-regex || true
 python3 -m pip install --no-cache --upgrade pip==22.2.2 setuptools==64.0.1

tests/end-to-end/test_completion.py

@@ -3,3 +3,7 @@ import subprocess
 
 def test_bash_completion_runs_without_error():
     subprocess.check_call('borgmatic --bash-completion | bash', shell=True)
+
+
+def test_fish_completion_runs_without_error():
+    subprocess.check_call('borgmatic --fish-completion | fish', shell=True)