diff --git a/src/testing/iotest/example_test.go b/src/testing/iotest/example_test.go
new file mode 100644
index 0000000000..10f6bd38f7
--- /dev/null
+++ b/src/testing/iotest/example_test.go
@@ -0,0 +1,22 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package iotest_test
+
+import (
+	"errors"
+	"fmt"
+	"testing/iotest"
+)
+
+func ExampleErrReader() {
+	// A reader that always returns a custom error.
+	r := iotest.ErrReader(errors.New("custom error"))
+	n, err := r.Read(nil)
+	fmt.Printf("n:   %d\nerr: %q\n", n, err)
+
+	// Output:
+	// n:   0
+	// err: "custom error"
+}
diff --git a/src/testing/iotest/logger_test.go b/src/testing/iotest/logger_test.go
index 575f37e05c..fec4467cc6 100644
--- a/src/testing/iotest/logger_test.go
+++ b/src/testing/iotest/logger_test.go
@@ -138,14 +138,14 @@ func TestReadLogger_errorOnRead(t *testing.T) {
 	data := []byte("Hello, World!")
 	p := make([]byte, len(data))
 
-	lr := ErrReader()
+	lr := ErrReader(errors.New("io failure"))
 	rl := NewReadLogger("read", lr)
 	n, err := rl.Read(p)
 	if err == nil {
 		t.Fatalf("Unexpectedly succeeded to read: %v", err)
 	}
 
-	wantLogWithHex := fmt.Sprintf("lr: read %x: %v\n", p[:n], "io")
+	wantLogWithHex := fmt.Sprintf("lr: read %x: io failure\n", p[:n])
 	if g, w := lOut.String(), wantLogWithHex; g != w {
 		t.Errorf("ReadLogger mismatch\n\tgot:  %q\n\twant: %q", g, w)
 	}
diff --git a/src/testing/iotest/reader.go b/src/testing/iotest/reader.go
index b18e912f27..bc2f72a911 100644
--- a/src/testing/iotest/reader.go
+++ b/src/testing/iotest/reader.go
@@ -88,16 +88,15 @@ 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)
+// ErrReader returns an io.Reader that returns 0, err from all Read calls.
+func ErrReader(err error) io.Reader {
+	return &alwaysErrReader{err: err}
 }
 
-type errReader int
-
-func (r errReader) Read(p []byte) (int, error) {
-	return 0, ErrIO
+type alwaysErrReader struct {
+	err error
+}
+
+func (aer *alwaysErrReader) Read(p []byte) (int, error) {
+	return 0, aer.err
 }
diff --git a/src/testing/iotest/reader_test.go b/src/testing/iotest/reader_test.go
index ccba22ee29..6004e841e5 100644
--- a/src/testing/iotest/reader_test.go
+++ b/src/testing/iotest/reader_test.go
@@ -6,6 +6,7 @@ package iotest
 
 import (
 	"bytes"
+	"errors"
 	"io"
 	"testing"
 )
@@ -226,11 +227,25 @@ func TestDataErrReader_emptyReader(t *testing.T) {
 }
 
 func TestErrReader(t *testing.T) {
-	n, err := ErrReader().Read([]byte{})
-	if err != ErrIO {
-		t.Errorf("ErrReader.Read(any) should have returned ErrIO, returned %v", err)
+	cases := []struct {
+		name string
+		err  error
+	}{
+		{"nil error", nil},
+		{"non-nil error", errors.New("io failure")},
+		{"io.EOF", io.EOF},
 	}
-	if n != 0 {
-		t.Errorf("ErrReader.Read(any) should have read 0 bytes, read %v", n)
+
+	for _, tt := range cases {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			n, err := ErrReader(tt.err).Read(nil)
+			if err != tt.err {
+				t.Fatalf("Error mismatch\nGot:  %v\nWant: %v", err, tt.err)
+			}
+			if n != 0 {
+				t.Fatalf("Byte count mismatch: got %d want 0", n)
+			}
+		})
 	}
 }