Added tests for StdWriter.Write.

The tests added cover the case when the Writer field returns and error
and, related to that, when the number of written bytes is less than 0.

Signed-off-by: Federico Gimenez <fgimenez@coit.es>
Upstream-commit: 3efe5ff22e7bf3264f653c7f7772c64771210afe
Component: engine

components/engine/pkg/stdcopy/stdcopy_test.go

@@ -2,6 +2,7 @@ package stdcopy
 
 import (
 	"bytes"
+	"errors"
 	"io/ioutil"
 	"strings"
 	"testing"
@@ -49,6 +50,41 @@ func TestWrite(t *testing.T) {
 	}
 }
 
+type errWriter struct {
+	n   int
+	err error
+}
+
+func (f *errWriter) Write(buf []byte) (int, error) {
+	return f.n, f.err
+}
+
+func TestWriteWithWriterError(t *testing.T) {
+	expectedError := errors.New("expected")
+	expectedReturnedBytes := 10
+	writer := NewStdWriter(&errWriter{
+		n:   stdWriterPrefixLen + expectedReturnedBytes,
+		err: expectedError}, Stdout)
+	data := []byte("This won't get written, sigh")
+	n, err := writer.Write(data)
+	if err != expectedError {
+		t.Fatalf("Didn't get expected error.")
+	}
+	if n != expectedReturnedBytes {
+		t.Fatalf("Didn't get expected writen bytes %d, got %d.",
+			expectedReturnedBytes, n)
+	}
+}
+
+func TestWriteDoesNotReturnNegativeWrittenBytes(t *testing.T) {
+	writer := NewStdWriter(&errWriter{n: -1}, Stdout)
+	data := []byte("This won't get written, sigh")
+	actual, _ := writer.Write(data)
+	if actual != 0 {
+		t.Fatalf("Expected returned written bytes equal to 0, got %d", actual)
+	}
+}
+
 func TestStdCopyWithInvalidInputHeader(t *testing.T) {
 	dstOut := NewStdWriter(ioutil.Discard, Stdout)
 	dstErr := NewStdWriter(ioutil.Discard, Stderr)