testing/iotest: add ErrReader

Adds an io.Reader that always returns 0 and a non-nil error.

Fixes #38781

Change-Id: I56bd124de07bc8809e77c6cfaab33a1e32cfe2ee
GitHub-Last-Rev: 4e232b17e9120405d4ea4743350ee361a3505043
GitHub-Pull-Request: golang/go#34741
Reviewed-on: https://go-review.googlesource.com/c/go/+/199501
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/testing/iotest/reader.go b/src/testing/iotest/reader.go
index 8d82018fd6..b18e912f27 100644
--- a/src/testing/iotest/reader.go
+++ b/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("io")
+
+// ErrReader returns a fake error every time it is read from.
+func ErrReader() io.Reader {
+	return errReader(0)
+}
+
+type errReader int
+
+func (r errReader) Read(p []byte) (int, error) {
+	return 0, ErrIO
+}