diff --git a/internal/errors/file.go b/internal/errors/file.go
index 267a6a0e5a..e5c6cc84ee 100644
--- a/internal/errors/file.go
+++ b/internal/errors/file.go
@@ -18,11 +18,14 @@
 package errors
 
 var (
+	// ErrWatchDirNotFound represents an error that the watch directory is not found.
 	ErrWatchDirNotFound = New("fs watcher watch dir not found")
 
+	// ErrFileAlreadyExists represents a function to generate an error that the file already exists.
 	ErrFileAlreadyExists = func(path string) error {
 		return Errorf("file already exists: %s", path)
 	}
 
+	// ErrPathNotSpecified represents an error that the path is not specified.
 	ErrPathNotSpecified = New("the path is not specified")
 )
diff --git a/internal/errors/file_test.go b/internal/errors/file_test.go
new file mode 100644
index 0000000000..80a4880aa6
--- /dev/null
+++ b/internal/errors/file_test.go
@@ -0,0 +1,174 @@
+//
+// Copyright (C) 2019-2020 Vdaas.org Vald team ( kpango, rinx, kmrmt )
+//
+// 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
+//
+//    https://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 errors
+
+import (
+	"testing"
+)
+
+func TestErrWatchDirNotFound(t *testing.T) {
+	type want struct {
+		want error
+	}
+	type test struct {
+		name       string
+		want       want
+		checkFunc  func(want, error) error
+		beforeFunc func()
+		afterFunc  func()
+	}
+	defaultCheckFunc := func(w want, got error) error {
+		if !Is(got, w.want) {
+			return Errorf("got: \"%#v\",\n\t\t\t\twant: \"%#v\"", got, w.want)
+		}
+		return nil
+	}
+	tests := []test{
+		{
+			name: "return ErrWatchDirNotFound error",
+			want: want{
+				want: New("fs watcher watch dir not found"),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(tt *testing.T) {
+			if test.beforeFunc != nil {
+				test.beforeFunc()
+			}
+			if test.afterFunc != nil {
+				defer test.afterFunc()
+			}
+			if test.checkFunc == nil {
+				test.checkFunc = defaultCheckFunc
+			}
+
+			got := ErrWatchDirNotFound
+			if err := test.checkFunc(test.want, got); err != nil {
+				tt.Errorf("error = %v", err)
+			}
+		})
+	}
+}
+
+func TestErrFileAlreadyExists(t *testing.T) {
+	type args struct {
+		path string
+	}
+	type want struct {
+		want error
+	}
+	type test struct {
+		name       string
+		args       args
+		want       want
+		checkFunc  func(want, error) error
+		beforeFunc func(args)
+		afterFunc  func(args)
+	}
+	defaultCheckFunc := func(w want, got error) error {
+		if !Is(got, w.want) {
+			return Errorf("got: \"%#v\",\n\t\t\t\twant: \"%#v\"", got, w.want)
+		}
+		return nil
+	}
+	tests := []test{
+		{
+			name: "return ErrFileAlreadyExists error with the file path is 'metadata.json'",
+			args: args{
+				path: "metadata.json",
+			},
+			want: want{
+				want: New("file already exists: metadata.json"),
+			},
+		},
+		{
+			name: "return ErrFileAlreadyExists error with the file path is empty",
+			args: args{
+				path: "",
+			},
+			want: want{
+				want: New("file already exists: "),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(tt *testing.T) {
+			if test.beforeFunc != nil {
+				test.beforeFunc(test.args)
+			}
+			if test.afterFunc != nil {
+				defer test.afterFunc(test.args)
+			}
+			if test.checkFunc == nil {
+				test.checkFunc = defaultCheckFunc
+			}
+
+			got := ErrFileAlreadyExists(test.args.path)
+			if err := test.checkFunc(test.want, got); err != nil {
+				tt.Errorf("error = %v", err)
+			}
+		})
+	}
+}
+
+func TestErrPathNotSpecified(t *testing.T) {
+	type want struct {
+		want error
+	}
+	type test struct {
+		name       string
+		want       want
+		checkFunc  func(want, error) error
+		beforeFunc func()
+		afterFunc  func()
+	}
+	defaultCheckFunc := func(w want, got error) error {
+		if !Is(got, w.want) {
+			return Errorf("got: \"%#v\",\n\t\t\t\twant: \"%#v\"", got, w.want)
+		}
+		return nil
+	}
+	tests := []test{
+		{
+			name: "return ErrPathNotSpecified error",
+			want: want{
+				want: New("the path is not specified"),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(tt *testing.T) {
+			if test.beforeFunc != nil {
+				test.beforeFunc()
+			}
+			if test.afterFunc != nil {
+				defer test.afterFunc()
+			}
+			if test.checkFunc == nil {
+				test.checkFunc = defaultCheckFunc
+			}
+
+			got := ErrPathNotSpecified
+			if err := test.checkFunc(test.want, got); err != nil {
+				tt.Errorf("error = %v", err)
+			}
+		})
+	}
+}