pkg: add new manifesttest package with test helpers

This commit adds a new `manifesttest` that helps sharing code
when testing generated osbuild manifests.

internal/manifesttest/manifesttest.go

@@ -0,0 +1,27 @@
+package manifesttest
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+// PipelineNamesFrom will return all pipeline names from an osbuild
+// json manifest. It will error on missing pipelines.
+//
+// TODO: move to images:pkg/manifesttest
+func PipelineNamesFrom(osbuildManifest []byte) ([]string, error) {
+	var manifest map[string]interface{}
+
+	if err := json.Unmarshal(osbuildManifest, &manifest); err != nil {
+		return nil, fmt.Errorf("cannot unmarshal manifest: %w", err)
+	}
+	if manifest["pipelines"] == nil {
+		return nil, fmt.Errorf("cannot find any pipelines in %v", manifest)
+	}
+	pipelines := manifest["pipelines"].([]interface{})
+	pipelineNames := make([]string, len(pipelines))
+	for idx, pi := range pipelines {
+		pipelineNames[idx] = pi.(map[string]interface{})["name"].(string)
+	}
+	return pipelineNames, nil
+}

internal/manifesttest/manifesttest_test.go

@@ -0,0 +1,35 @@
+package manifesttest_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/osbuild/image-builder-cli/internal/manifesttest"
+)
+
+var fakeOsbuildManifest = `{
+  "version": "2",
+  "pipelines": [
+    {
+       "name": "noop"
+    },
+    {
+       "name": "noop2"
+    }
+  ]
+}`
+
+func TestPipelineNamesFrom(t *testing.T) {
+	names, err := manifesttest.PipelineNamesFrom([]byte(fakeOsbuildManifest))
+	assert.NoError(t, err)
+	assert.Equal(t, []string{"noop", "noop2"}, names)
+}
+
+func TestPipelineNamesFromSad(t *testing.T) {
+	_, err := manifesttest.PipelineNamesFrom([]byte("bad-json"))
+	assert.ErrorContains(t, err, "cannot unmarshal manifest: invalid char")
+
+	_, err = manifesttest.PipelineNamesFrom([]byte("{}"))
+	assert.ErrorContains(t, err, "cannot find any pipelines in map[]")
+}