Add unit test for groups stage

Refs: #405

internal/osbuild/groups_stage_test.go

@@ -0,0 +1,16 @@
+package osbuild
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewGroupsStage(t *testing.T) {
+	expectedStage := &Stage{
+		Name:    "org.osbuild.groups",
+		Options: &GroupsStageOptions{},
+	}
+	actualStage := NewGroupsStage(&GroupsStageOptions{})
+	assert.Equal(t, expectedStage, actualStage)
+}