testing/iotest: add FailReader

Signed-off-by: Carlos Alexandro Becker <caarlos0@gmail.com>

Author: caarlos0

src/testing/iotest/reader.go

@@ -68,6 +68,7 @@ func (r *dataErrReader) Read(p []byte) (n int, err error) {
 	return
 }
 
+// ErrTimeout is a fake timeout error
 var ErrTimeout = errors.New("timeout")
 
 // TimeoutReader returns ErrTimeout on the second read
@@ -86,3 +87,17 @@ func (r *timeoutReader) Read(p []byte) (int, error) {
 	}
 	return r.r.Read(p)
 }
+
+// ErrIO is a fake IO error
+var ErrIO = errors.New("fake io error")
+
+// FailReader returns a fake error every time it is read from.
+func FailReader() io.Reader {
+	return &failReader{}
+}
+
+type failReader struct{}
+
+func (r *failReader) Read(p []byte) (int, error) {
+	return 0, ErrIO
+}

src/testing/iotest/reader_test.go

@@ -0,0 +1,16 @@
+package iotest
+
+import (
+	"testing"
+	"testing/iotest"
+)
+
+func TestFailReader(t *testing.T) {
+	read, err := iotest.FailReader().Read([]byte{})
+	if err != iotest.ErrIO {
+		t.Errorf("FailReader.Read(any) should have returned ErrIO, returned %v", err)
+	}
+	if read != 0 {
+		t.Errorf("FailReader.Read(any) should have read 0 bytes, read %v", read)
+	}
+}