chore(examples): add tests for preferskipoptionalpointer

As part of a future change, we're adding the Output Option
`prefer-skip-optional-pointer-with-omitzero`.

As part of this, we want to make sure that the existing behaviour, with
the `omitempty` default, works as expected.

Author: Jamie Tanna

examples/output-options/preferskipoptionalpointer/gen_test.go

@@ -0,0 +1,65 @@
+package preferskipoptionalpointer
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestClient(t *testing.T) {
+	t.Run("zero value (empty string) on Name is not omitted", func(t *testing.T) {
+		client := Client{
+			Name: "",
+		}
+
+		b, err := json.Marshal(client)
+		require.NoError(t, err)
+
+		assert.True(t, jsonContainsKey(b, "name"))
+	})
+
+	t.Run("value on Name is not omitted", func(t *testing.T) {
+		client := Client{
+			Name: "some value",
+		}
+
+		b, err := json.Marshal(client)
+		require.NoError(t, err)
+
+		assert.True(t, jsonContainsKey(b, "name"))
+	})
+
+	t.Run("zero value (0.0) on Id is omitted (as `omitempty` flags it as empty)", func(t *testing.T) {
+		client := Client{
+			Id: 0.0,
+		}
+
+		b, err := json.Marshal(client)
+		require.NoError(t, err)
+
+		assert.False(t, jsonContainsKey(b, "id"))
+	})
+
+	t.Run("value on Id is not omitted", func(t *testing.T) {
+		client := Client{
+			Id: 3.142,
+		}
+
+		b, err := json.Marshal(client)
+		require.NoError(t, err)
+
+		assert.True(t, jsonContainsKey(b, "id"))
+	})
+}
+
+// jsonContainsKey checks if the given JSON object contains the specified key at the top level.
+func jsonContainsKey(b []byte, key string) bool {
+	var m map[string]any
+	if err := json.Unmarshal(b, &m); err != nil {
+		return false
+	}
+	_, ok := m[key]
+	return ok
+}