Add tests for every implemented command

tests/service_list.bats

@@ -0,0 +1,28 @@
+#!/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 "($PLUGIN_COMMAND_PREFIX:list) with no exposed ports" {
+  run dokku "$PLUGIN_COMMAND_PREFIX:list"
+  assert_contains "${lines[*]}" "l (running)"
+}
+
+@test "($PLUGIN_COMMAND_PREFIX:list) with exposed ports" {
+  dokku "$PLUGIN_COMMAND_PREFIX:expose" l 4242
+  run dokku "$PLUGIN_COMMAND_PREFIX:list"
+  assert_contains "${lines[*]}" "l (running), exposed port(s): 5432->4242"
+}
+
+@test "($PLUGIN_COMMAND_PREFIX:list) when there are no services" {
+  dokku --force "$PLUGIN_COMMAND_PREFIX:destroy" l >&2
+  run dokku "$PLUGIN_COMMAND_PREFIX:list"
+  assert_contains "${lines[*]}" "There are no Postgres services"
+  dokku "$PLUGIN_COMMAND_PREFIX:create" l >&2
+}