diff --git a/internal/datafs/envfs_test.go b/internal/datafs/envfs_test.go
index cb1fce695..d8bfd092b 100644
--- a/internal/datafs/envfs_test.go
+++ b/internal/datafs/envfs_test.go
@@ -71,6 +71,8 @@ func TestEnvFile_Stat(t *testing.T) {
 }
 
 func TestEnvFS(t *testing.T) {
+	t.Cleanup(func() { environ = os.Environ })
+
 	u, _ := url.Parse("env:")
 
 	lfsys := fstest.MapFS{}
@@ -96,7 +98,7 @@ func TestEnvFS(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, "hello world", string(b))
 
-	assert.NoError(t, fstest.TestFS(fsys, "FOO", "FOO_FILE", "HOME"))
+	assert.NoError(t, fstest.TestFS(fsys, "FOO", "FOO_FILE"))
 }
 
 func TestEnvFile_ReadDir(t *testing.T) {
diff --git a/internal/datafs/fsys_test.go b/internal/datafs/fsys_test.go
index ca30f9120..269c4d72f 100644
--- a/internal/datafs/fsys_test.go
+++ b/internal/datafs/fsys_test.go
@@ -15,6 +15,8 @@ import (
 )
 
 func TestFSysForPath(t *testing.T) {
+	vol, _, _ := getVolWd()
+
 	t.Run("no provider", func(t *testing.T) {
 		ctx := ContextWithFSProvider(context.Background(), nil)
 		_, err := FSysForPath(ctx, "foo")
@@ -29,12 +31,12 @@ func TestFSysForPath(t *testing.T) {
 			assert.Equal(t, "file", u.Scheme)
 
 			if runtime.GOOS == "windows" {
-				assert.Equal(t, "C:/tmp/foo/", u.Path)
-				return os.DirFS("C:/tmp/foo/"), nil
+				assert.Equal(t, vol+"/tmp/foo/", u.Path)
+				return os.DirFS(vol + "/"), nil
 			}
 
 			assert.Equal(t, "/tmp/foo", u.Path)
-			return os.DirFS("/tmp/foo"), nil
+			return os.DirFS("/"), nil
 		}, "file")
 
 		ctx := ContextWithFSProvider(context.Background(), fsp)
@@ -60,7 +62,7 @@ func TestFSysForPath(t *testing.T) {
 		fsp := fsimpl.FSProviderFunc(func(u *url.URL) (fs.FS, error) {
 			assert.Equal(t, "git+file", u.Scheme)
 			if runtime.GOOS == "windows" {
-				assert.Equal(t, "C:/tmp/repo/", u.Path)
+				assert.Equal(t, vol+"/tmp/repo/", u.Path)
 			} else {
 				assert.Equal(t, "/tmp/repo", u.Path)
 			}
diff --git a/internal/datafs/wdfs.go b/internal/datafs/wdfs.go
index 38a2c8ed6..20cef0679 100644
--- a/internal/datafs/wdfs.go
+++ b/internal/datafs/wdfs.go
@@ -31,7 +31,7 @@ func ResolveLocalPath(fsys fs.FS, name string) (root, resolved string, err error
 	default:
 	}
 
-	vol, wd, err := getWdVol()
+	vol, wd, err := getVolWd()
 	if err != nil {
 		return "", "", err
 	}
@@ -40,7 +40,9 @@ func ResolveLocalPath(fsys fs.FS, name string) (root, resolved string, err error
 	return f.resolveLocalPath(name)
 }
 
-func getWdVol() (string, string, error) {
+// getVolWd - returns the volume name and current working directory, or "/" if
+// the current working directory has no volume name (e.g. on Unix).
+func getVolWd() (string, string, error) {
 	wd, err := os.Getwd()
 	if err != nil {
 		return "", "", fmt.Errorf("getwd: %w", err)
@@ -208,7 +210,7 @@ var WdFS = fsimpl.FSProviderFunc(
 			return nil, fmt.Errorf("unsupported path %q: %w", u.Path, fs.ErrInvalid)
 		}
 
-		vol, wd, _ := getWdVol()
+		vol, wd, _ := getVolWd()
 
 		var fsys fs.FS
 		if vol == "" || vol == "/" {
@@ -237,7 +239,7 @@ func WrapWdFS(fsys fs.FS) fs.FS {
 		return fsys
 	}
 
-	vol, wd, _ := getWdVol()
+	vol, wd, _ := getVolWd()
 
 	return &wdFS{fsys: fsys, vol: vol, wd: wd}
 }