internal/multierror: add tests

Signed-off-by: Andrew Keesler <ankeesler1@gmail.com>

internal/multierror/multierror.go

@@ -1,6 +1,15 @@
 // Copyright 2020 the Pinniped contributors. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0
 
+// Package multierror provides a type that can translate multiple errors into a Go error interface.
+//
+// A common use of this package is as follows.
+//   errs := multierror.New()
+//   for i := range stuff {
+//     err := doThing(i)
+//     errs.Add(err)
+//   }
+//   return errs.ErrOrNil()
 package multierror
 
 import (
@@ -8,31 +17,34 @@ import (
 	"strings"
 )
 
-type multiError []error
+// MultiError holds a list of error's, that could potentially be empty.
+//
+// Use New() to create a MultiError.
+type MultiError []error
 
-func New() multiError { //nolint:golint // returning a private type for encapsulation purposes
+// New returns an empty MultiError.
+func New() MultiError {
 	return make([]error, 0)
 }
 
-func (m *multiError) Add(err error) {
+// Add adds an error to the MultiError. The provided err must not be nil.
+func (m *MultiError) Add(err error) {
 	*m = append(*m, err)
 }
 
-func (m multiError) len() int {
-	return len(m)
-}
-
-func (m multiError) Error() string {
+// Error implements the error.Error() interface method.
+func (m MultiError) Error() string {
 	sb := strings.Builder{}
-	_, _ = fmt.Fprintf(&sb, "%d errors:", m.len())
+	_, _ = fmt.Fprintf(&sb, "%d error(s):", len(m))
 	for _, err := range m {
 		_, _ = fmt.Fprintf(&sb, "\n- %s", err.Error())
 	}
 	return sb.String()
 }
 
-func (m multiError) ErrOrNil() error {
-	if m.len() > 0 {
+// ErrOrNil returns either nil, if there are no errors in this MultiError, or an error, otherwise.
+func (m MultiError) ErrOrNil() error {
+	if len(m) > 0 {
 		return m
 	}
 	return nil

internal/multierror/multierror_test.go

@@ -0,0 +1,24 @@
+// Copyright 2020 the Pinniped contributors. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package multierror
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestMultierror(t *testing.T) {
+	errs := New()
+
+	require.Nil(t, errs.ErrOrNil())
+
+	errs.Add(errors.New("some error 1"))
+	require.EqualError(t, errs.ErrOrNil(), "1 error(s):\n- some error 1")
+
+	errs.Add(errors.New("some error 2"))
+	errs.Add(errors.New("some error 3"))
+	require.EqualError(t, errs.ErrOrNil(), "3 error(s):\n- some error 1\n- some error 2\n- some error 3")
+}