structs: add tests for String() methods

To show that printing one of these IDs works properly now that the String() method
receiver is no longer a pointer.

agent/structs/structs_oss_test.go

@@ -0,0 +1,41 @@
+package structs
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestServiceID_String(t *testing.T) {
+	t.Run("value", func(t *testing.T) {
+		sid := NewServiceID("the-id", &EnterpriseMeta{})
+		require.Equal(t, "the-id", fmt.Sprintf("%v", sid))
+	})
+	t.Run("pointer", func(t *testing.T) {
+		sid := NewServiceID("the-id", &EnterpriseMeta{})
+		require.Equal(t, "the-id", fmt.Sprintf("%v", &sid))
+	})
+}
+
+func TestCheckID_String(t *testing.T) {
+	t.Run("value", func(t *testing.T) {
+		cid := NewCheckID("the-id", &EnterpriseMeta{})
+		require.Equal(t, "the-id", fmt.Sprintf("%v", cid))
+	})
+	t.Run("pointer", func(t *testing.T) {
+		cid := NewCheckID("the-id", &EnterpriseMeta{})
+		require.Equal(t, "the-id", fmt.Sprintf("%v", &cid))
+	})
+}
+
+func TestServiceName_String(t *testing.T) {
+	t.Run("value", func(t *testing.T) {
+		sn := NewServiceName("the-id", &EnterpriseMeta{})
+		require.Equal(t, "the-id", fmt.Sprintf("%v", sn))
+	})
+	t.Run("pointer", func(t *testing.T) {
+		sn := NewServiceName("the-id", &EnterpriseMeta{})
+		require.Equal(t, "the-id", fmt.Sprintf("%v", &sn))
+	})
+}