fs test run error at windows

[linlexing]

The following program sample.go triggers an unexpected result

package main

import (
    "testing/fstest"

    "github.com/traefik/yaegi/interp"
    "github.com/traefik/yaegi/stdlib"
)

var testFilesystem = fstest.MapFS{
    "main.go": &fstest.MapFile{
        Data: []byte(`package main

import (
    "foo/bar"
    "./localfoo"
)

func main() {
    bar.PrintSomething()
    localfoo.PrintSomethingElse()
}
`),
    },
    `_pkg/src/foo/bar/bar.go`: &fstest.MapFile{
        Data: []byte(`package bar

import (
    "fmt"
)

func PrintSomething() {
    fmt.Println("I am a virtual filesystem printing something from _pkg/src/foo/bar/bar.go!")
}
`),
    },
    `localfoo/foo.go`: &fstest.MapFile{
        Data: []byte(`package localfoo

import (
    "fmt"
)

func PrintSomethingElse() {
    fmt.Println("I am virtual filesystem printing else from localfoo/foo.go!")
}
`),
    },
}

func main() {
    i := interp.New(interp.Options{
        GoPath:               "./_pkg",
        SourcecodeFilesystem: testFilesystem,
    })
    if err := i.Use(stdlib.Symbols); err != nil {
        panic(err)
    }

    _, err := i.EvalPath(`main.go`)
    if err != nil {
        panic(err)
    }
}

Expected result

I am a virtual filesystem printing something from _pkg/src/foo/bar/bar.go!
I am virtual filesystem printing else from localfoo/foo.go!

Got

panic: main.go:4:2: import "foo/bar" error: package location C:\gosrc\src\test not in GOPATH

Yaegi Version

v0.15.1

Additional Notes

fstest uses the character / as the separator, while the internal Interpreter.pkgDir function combines paths with filepath.Join, but on windows, the path separator uses the character \, causing this error.