adding unit test for error scenario in internal/credential/store.go file

Signed-off-by: Akanksha Gahalot <akankshagahlot0307@gmail.com>

internal/credential/store.go

@@ -19,6 +19,8 @@ import (
 	credentials "github.com/oras-project/oras-credentials-go"
 )
 
+var CreateNewStore = credentials.NewStore
+
 // NewStore generates a store based on the passed-in config file paths.
 func NewStore(configPaths ...string) (credentials.Store, error) {
 	opts := credentials.StoreOptions{AllowPlaintextPut: true}
@@ -29,7 +31,7 @@ func NewStore(configPaths ...string) (credentials.Store, error) {
 
 	var stores []credentials.Store
 	for _, config := range configPaths {
-		store, err := credentials.NewStore(config, opts)
+		store, err := CreateNewStore(config, opts)
 		if err != nil {
 			return nil, err
 		}

internal/credential/store_test.go

@@ -0,0 +1,40 @@
+/*
+Copyright The ORAS Authors.
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package credential
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+
+	credentials "github.com/oras-project/oras-credentials-go"
+)
+
+func TestNewStoreError(t *testing.T) {
+	// save current function
+	oldFunction := CreateNewStore
+	// restoring changes
+	defer func() { CreateNewStore = oldFunction }()
+	CreateNewStore = func(configPath string, opts credentials.StoreOptions) (credentials.Store, error) {
+		return nil, fmt.Errorf("New Error")
+	}
+	var config string = "testconfig"
+	credStore, err := NewStore(config)
+	if !reflect.DeepEqual(credStore, nil) {
+		t.Errorf("Expected NewStore to return nil but actually returned %v ", credStore)
+	}
+	if reflect.DeepEqual(err, nil) {
+		t.Error("Expected Error to be not nil but actually returned nil ")
+	}
+}