Add ppx error test

Author: cristianoc

tests/tools_tests/ppx/TestPpx.res

@@ -24,3 +24,8 @@ module Arity = {
   let two = (x, y) => x + y
   let n = two(one(1), 5)
 }
+
+@module("react")
+external useState: (unit => 'state) => string = "useState"
+
+let _ = useState(() => 0)

tests/tools_tests/src/expected/TestPpx.res.jsout

@@ -1,45 +0,0 @@
-// Generated by ReScript, PLEASE EDIT WITH CARE
-'use strict';
-
-
-console.log("ppx test");
-
-console.log("ppx test");
-
-let M = {
-  v: 10
-};
-
-let OptionalFields = {
-  r: {
-    y: 1.0
-  }
-};
-
-function one(x) {
-  return x;
-}
-
-function two(x, y) {
-  return x + y | 0;
-}
-
-let Arity = {
-  one: one,
-  two: two,
-  n: 6
-};
-
-let a = "A";
-
-let b = "B";
-
-let vv = 10;
-
-exports.a = a;
-exports.b = b;
-exports.M = M;
-exports.vv = vv;
-exports.OptionalFields = OptionalFields;
-exports.Arity = Arity;
-/*  Not a pure module */