Add tests for every implemented command

tests/service_unlink.bats

@@ -0,0 +1,39 @@
+#!/usr/bin/env bats
+load test_helper
+
+setup() {
+  dokku apps:create my_app >&2
+  dokku "$PLUGIN_COMMAND_PREFIX:create" l >&2
+}
+
+teardown() {
+  dokku --force "$PLUGIN_COMMAND_PREFIX:destroy" l >&2
+  rm "$DOKKU_ROOT/my_app" -rf
+}
+
+@test "($PLUGIN_COMMAND_PREFIX:unlink) error when there are no arguments" {
+  run dokku "$PLUGIN_COMMAND_PREFIX:unlink"
+  assert_contains "${lines[*]}" "Please specify a name for the service"
+}
+
+@test "($PLUGIN_COMMAND_PREFIX:unlink) error when the app argument is missing" {
+  run dokku "$PLUGIN_COMMAND_PREFIX:unlink" l
+  assert_contains "${lines[*]}" "Please specify an app to run the command on"
+}
+
+@test "($PLUGIN_COMMAND_PREFIX:unlink) error when the app does not exist" {
+  run dokku "$PLUGIN_COMMAND_PREFIX:unlink" l not_existing_app
+  assert_contains "${lines[*]}" "App not_existing_app does not exist"
+}
+
+@test "($PLUGIN_COMMAND_PREFIX:unlink) error when the service does not exist" {
+  run dokku "$PLUGIN_COMMAND_PREFIX:unlink" not_existing_service my_app
+  assert_contains "${lines[*]}" "service not_existing_service does not exist"
+}
+
+@test "($PLUGIN_COMMAND_PREFIX:unlink) success" {
+  dokku "$PLUGIN_COMMAND_PREFIX:link" l my_app >&2
+  run dokku "$PLUGIN_COMMAND_PREFIX:unlink" l my_app
+  links=$(cat "$PLUGIN_DATA_ROOT/l/LINKS")
+  assert_equal "$links" ""
+}