Add tests for every implemented command

tests/service_start.bats

@@ -0,0 +1,26 @@
+#!/usr/bin/env bats
+load test_helper
+
+setup() {
+  dokku "$PLUGIN_COMMAND_PREFIX:create" l >&2
+}
+
+teardown() {
+  dokku --force "$PLUGIN_COMMAND_PREFIX:destroy" l >&2
+}
+
+@test "($PLUGIN_COMMAND_PREFIX:start) error when there are no arguments" {
+  run dokku "$PLUGIN_COMMAND_PREFIX:start"
+  assert_contains "${lines[*]}" "Please specify a name for the service"
+}
+
+@test "($PLUGIN_COMMAND_PREFIX:start) error when service does not exist" {
+  run dokku "$PLUGIN_COMMAND_PREFIX:start" not_existing_service
+  assert_contains "${lines[*]}" "service not_existing_service does not exist"
+}
+
+@test "($PLUGIN_COMMAND_PREFIX:start) success" {
+  run dokku "$PLUGIN_COMMAND_PREFIX:start" l
+  assert_success
+}
+