Implement reader and writer that return errors

test.go

@@ -0,0 +1,52 @@
+package test
+
+import "errors"
+
+// ErrPlain is the default error that is returned for functions in this package.
+var ErrPlain = errors.New("error")
+
+////////////////
+
+// ErrorReader implements an io.Reader that will do N successive reads before it returns ErrPlain.
+type ErrorReader struct {
+	n int
+}
+
+// NewErrorReader returns a new ErrorReader.
+func NewErrorReader(n int) *ErrorReader {
+	return &ErrorReader{n}
+}
+
+// Read implements the io.Reader interface.
+func (r *ErrorReader) Read(b []byte) (n int, err error) {
+	if len(b) == 0 {
+		return 0, nil
+	}
+	if r.n == 0 {
+		return 0, ErrPlain
+	}
+	r.n--
+	b[0] = '.'
+	return 1, nil
+}
+
+////////////////
+
+// ErrorWriter implements an io.Writer that will do N successive writes before it returns ErrPlain.
+type ErrorWriter struct {
+	n int
+}
+
+// NewErrorWriter returns a new ErrorWriter.
+func NewErrorWriter(n int) *ErrorWriter {
+	return &ErrorWriter{n}
+}
+
+// Write implements the io.Writer interface.
+func (w *ErrorWriter) Write(b []byte) (n int, err error) {
+	if w.n == 0 {
+		return 0, ErrPlain
+	}
+	w.n--
+	return len(b), nil
+}