Add print test coverage

Signed-off-by: Terry Howe <[email protected]>

cmd/oras/internal/display/status/print.go

@@ -47,11 +47,9 @@ func (p *Printer) Println(a ...any) {
 	p.lock.Lock()
 	defer p.lock.Unlock()
 	_, err := fmt.Fprintln(p.out, a...)
-	if err != nil {
-		if p.errored == nil {
-			p.errored = fmt.Errorf("display output error: %w", err)
-			_, _ = fmt.Fprint(os.Stderr, p.errored)
-		}
+	if err != nil && p.errored == nil {
+		p.errored = fmt.Errorf("display output error: %w", err)
+		_, _ = fmt.Fprint(os.Stderr, p.errored)
 	}
 }
 

cmd/oras/internal/display/status/print_test.go

@@ -0,0 +1,63 @@
+/*
+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 status
+
+import (
+	"fmt"
+	"io"
+	"strings"
+	"testing"
+)
+
+type mockWriter struct{}
+
+func (mw *mockWriter) Write(p []byte) (n int, err error) {
+	return 0, fmt.Errorf("Boom: " + string(p))
+}
+
+func TestPrint_Error(t *testing.T) {
+	foo := &mockWriter{}
+	printer := NewPrinter(foo)
+	printer.Println("one")
+	if printer.errored == nil {
+		t.Error("Print should error")
+	}
+	if printer.errored.Error() == "Boom: one" {
+		t.Error("Unexpected error text: " + printer.errored.Error())
+	}
+
+	printer.Println("two")
+	if printer.errored == nil {
+		t.Error("Print should still error")
+	}
+	if printer.errored.Error() == "Boom: one" {
+		t.Error("Unexpected error text second time: " + printer.errored.Error())
+	}
+}
+
+func TestPrint_NoError(t *testing.T) {
+	var ser strings.Builder
+	printer := NewPrinter(io.Writer(&ser))
+	expected := "blah blah"
+	printer.Println(expected)
+	if printer.errored != nil {
+		t.Error("Print should not error")
+	}
+	actual := strings.TrimSpace(ser.String())
+	if expected != actual {
+		t.Error("Expected <" + expected + "> not equal to actual <" + actual + ">")
+	}
+}