fix test

src/cmd/go/testdata/script/build_relative_import_not_supported_in_go_path_mode.txt

@@ -1,11 +1,27 @@
 env GO111MODULE=off
 
-! go build
-stderr 'cannot find package "\." in:\n\t.WORK/gopath/src/foo'
+# Control case: in GOPATH mode,
+# a/a.go can import package "./b" using a relative path.
+go build a/a.go
+! stderr .
 
--- main.go --
-package main
+# package "a" itself cannot import "./b": "a" has a non-local
+# import path, so its imports must also have non-local import paths.
+! go build a
+stderr '^a[/\\]a.go:3:8: local import "./b" in non-local package$'
 
-import _ "./foo"
+# package "c" imports itself, which is not allowed.
+! go build c
+stderr '^c[/\\]c.go:3:8: .: cannot import current directory$'
 
-func main() {}
+
+-- a/a.go --
+package a
+
+import _ "./b"
+-- a/b/b.go --
+package b
+-- c/c.go --
+package c
+
+import _ "."