Refactor storage tests (#727)

* Refactor storage tests

* minio: check object err

* remove inaccurate test

* storage/fs: use memory

pkg/storage/mongo/mongo_test.go

@@ -0,0 +1,38 @@
+package mongo
+
+import (
+	"os"
+	"testing"
+
+	"github.com/gomods/athens/pkg/config"
+	"github.com/gomods/athens/pkg/storage/compliance"
+	"github.com/stretchr/testify/require"
+)
+
+func TestBackend(t *testing.T) {
+	backend := getStorage(t)
+	compliance.RunTests(t, backend, backend.clear)
+}
+
+func (m *ModuleStore) clear() error {
+	m.s.DB(m.d).C(m.c).DropCollection()
+
+	return m.initDatabase()
+}
+
+func BenchmarkBackend(b *testing.B) {
+	backend := getStorage(b)
+	compliance.RunBenchmarks(b, backend, backend.clear)
+}
+
+func getStorage(tb testing.TB) *ModuleStore {
+	url := os.Getenv("ATHENS_MONGO_URL")
+	if url == "" {
+		tb.SkipNow()
+	}
+
+	backend, err := NewStorage(&config.MongoConfig{URL: url})
+	require.NoError(tb, err)
+
+	return backend
+}