You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: context_fs_test.go
    path of file: ./repos/echo
    
    the code of the file until where you have to start completion: // SPDX-License-Identifier: MIT
// SPDX-FileCopyrightText: Â© 2015 LabStack LLC and Echo contributors

package echo

import (
	"github.com/stretchr/testify/assert"
	"io/fs"
	"net/http"
	"net/http/httptest"
	"os"
	"testing"
)

func TestContext_File(t *testing.T) {
	var testCases = []struct {
		name             string
		whenFile         string
		whenFS           fs.FS
		expectStatus     int
		expectStartsWith []byte
		expectError      string
	}{
		{
			name:             "ok, from default file system",
			whenFile:         "_fixture/images/walle.png",
			whenFS:           nil,
			expectStatus:     http.StatusOK,
			expectStartsWith: []byte{0x89, 0x50, 0x4e},
		},
		{
			name:             "ok, from custom file system",
			whenFile:         "walle.png",
			whenFS:           os.DirFS("_fixture/images"),
			expectStatus:     http.StatusOK,
			expectStartsWith: []byte{0x89, 0x50, 0x4e},
		},
		{
			name:             "nok, not existent file",
			whenFile:         "not.png",
			whenFS:           os.DirFS("_fixture/
    
func TestContext_FileFS(t *testing.T) {
	var testCases = []struct {
		name             string
		whenFile         string
		whenFS           fs.FS
		expectStatus     int
		expectStartsWith []byte
		expectError      string
	}{
		{
			name:             "ok",
			whenFile:         "walle.png",
			whenFS:           os.DirFS("_fixture/images"),
			expectStatus:     http.StatusOK,
			expectStartsWith: []byte{0x89, 0x50, 0x4e},
		},
		{
			name:             "nok, not existent file",
			whenFile:         "not.png",
			whenFS:           os.DirFS("_fixture/images"),
			expectStatus:     http.StatusOK,
			expectStartsWith: nil,
			expectError:      "code=404, message=Not Found",
		},
	}

	for _, tc := range testCases {
		t.Run(tc.name, func(t *testing.T) {
			e := New()

			handler := func(ec Context) error {
				return ec.(*context).FileFS(tc.whenFile, tc.whenFS)
			}

			req := httptest.NewRequest(http.MethodGet, "/match.png", nil)
			rec := httptest.NewRecorder()
			c := e.NewContext(req, rec)

			err := handler(c)

			assert.Equal(t, tc.expectStatus, rec.Code)
			if tc.expectError != "" {
				assert.EqualError(t, err, tc.expectError)
			} else {
				assert.NoError(t, err)
			}

			body := rec.Body.Bytes()
			if len(body) > len(tc.expectStartsWith) {
				body = body[:len(tc.expectStartsWith)]
			}
			assert.Equal(t, tc.expectStartsWith, body)
		})
	}
}