v.pref: fix vsh_envbang_test.v to always use the local V executable (#22563)

vlib/v/pref/vsh_envbang_test.v

@@ -1,11 +1,22 @@
 import os
 import rand
 
-fn test_envbang_script_runs() {
+const vexe = @VEXE
-	env_location := '/usr/bin/env'
+
+fn testsuite_begin() {
 	$if windows {
 		skip_test('windows does not support envbang lines')
 	}
+	// Make sure, that we will be using the local v, instead of the globally installed one,
+	// for the rest of the tests here:
+	local_v_path := os.dir(vexe)
+	old_path := os.getenv('PATH')
+	os.setenv('PATH', '${local_v_path}:${old_path}', true)
+	println('Changed PATH: ${os.getenv('PATH')}')
+}
+
+fn test_envbang_script_runs() {
+	env_location := '/usr/bin/env'
 	if !os.exists(env_location) {
 		skip_test('${env_location} does not exist')
 	}
@@ -18,14 +29,18 @@ fn test_envbang_script_runs() {
 	os.write_file(rnd_vsh_script_path, "#!${env_location} v
 import os
 println('hello')
+println('@VEXE: ${vexe}')
 println(os.args)
 ")!
 	os.chmod(rnd_vsh_script_path, 0o700)!
 	res := os.execute('${os.quoted_path(rnd_vsh_script_path)} abc 123 -option')
 	assert res.exit_code == 0
 	lines := res.output.split_into_lines()
+	dump(lines)
 	assert lines[0] == 'hello'
-	assert lines[1].ends_with(", 'abc', '123', '-option']")
+	assert lines[1].starts_with('@VEXE: ')
+	assert os.real_path(lines[1].all_after('@VEXE: ')) == os.real_path(vexe)
+	assert lines[2].ends_with(", 'abc', '123', '-option']")
 	os.rm(rnd_vsh_script_path)!
 }