increase coverage

Signed-off-by: Xiaoxuan Wang <wangxiaoxuan119@gmail.com>

cmd/oras/internal/display/metadata/text/push_test.go

@@ -0,0 +1,74 @@
+/*
+Copyright The ORAS Authors.
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package text
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"testing"
+
+	"github.com/opencontainers/go-digest"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+// errorWriter implements the io.Writer interface returns an error in Write.
+type errorWriter struct{}
+
+func (w *errorWriter) Write(p []byte) (n int, err error) {
+	return 0, fmt.Errorf("got an error")
+}
+
+func TestPushHandler_OnCompleted(t *testing.T) {
+	content := []byte("content")
+	tests := []struct {
+		name    string
+		out     io.Writer
+		root    ocispec.Descriptor
+		wantErr bool
+	}{
+		{
+			"good path",
+			&bytes.Buffer{},
+			ocispec.Descriptor{
+				MediaType: "example",
+				Digest:    digest.FromBytes(content),
+				Size:      int64(len(content)),
+			},
+			false,
+		},
+		{
+			"error path",
+			&errorWriter{},
+			ocispec.Descriptor{
+				MediaType: "example",
+				Digest:    digest.FromBytes(content),
+				Size:      int64(len(content)),
+			},
+			true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			p := &PushHandler{
+				out: tt.out,
+			}
+			if err := p.OnCompleted(tt.root); (err != nil) != tt.wantErr {
+				t.Errorf("PushHandler.OnCompleted() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}