tests: fix repl_test.v

vlib/v/builder/compile.v

@@ -265,7 +265,12 @@ pub fn (v &Builder) get_user_files() []string {
 		user_files << single_test_v_file
 		dir = os.base_dir(single_test_v_file)
 	}
-	is_real_file := os.exists(dir) && !os.is_dir(dir)
+	does_exist := os.exists(dir)
+	if !does_exist {
+		verror("$dir doesn't exist")
+		exit(1)
+	}
+	is_real_file := does_exist && !os.is_dir(dir)
 	if is_real_file && (dir.ends_with('.v') || dir.ends_with('.vsh') || dir.ends_with('.vv')) {
 		single_v_file := dir
 		// Just compile one file and get parent dir

vlib/v/tests/repl/repl_test.v

@@ -21,7 +21,8 @@ fn test_the_v_compiler_can_be_invoked() {
 	}
 	// println('"$vcmd_error" exit_code: $r_error.exit_code | output: $r_error.output')
 	assert r_error.exit_code == 1
-	assert r_error.output.trim_space() == "builder error: nonexisting.v doesn't exist"
+	actual_error := r_error.output.trim_space()
+	assert actual_error == "builder error: nonexisting.v doesn't exist"
 }
 
 struct Session {