test: test doc'd napi_get_value_int32 behaviour

We chose to document this in the docs as there are
different possible behaviours.  Adding this test to validate
that all vm implementations do it the same way.

PR-URL: #12633
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/addons-napi/test_number/test.js

@@ -37,3 +37,11 @@ assert.strictEqual(num7, test_number.Test(num7));
 
 const num8 = Number.NEGATIVE_INFINITY;
 assert.strictEqual(num8, test_number.Test(num8));
+
+
+// validate documented behaviour when value is retrieved
+// as 32 bit integer with napi_get_value_int32
+assert.strictEqual(1, test_number.TestInt32Truncation(4294967297));
+assert.strictEqual(0, test_number.TestInt32Truncation(4294967296));
+assert.strictEqual(-1, test_number.TestInt32Truncation(4294967295));
+assert.strictEqual(3, test_number.TestInt32Truncation(4294967296 * 5 + 3));

test/addons-napi/test_number/test_number.c

@@ -23,9 +23,32 @@ napi_value Test(napi_env env, napi_callback_info info) {
   return output;
 }
 
+napi_value TestInt32Truncation(napi_env env, napi_callback_info info) {
+  size_t argc = 1;
+  napi_value args[1];
+  NAPI_CALL(env, napi_get_cb_info(env, info, &argc, args, NULL, NULL));
+
+  NAPI_ASSERT(env, argc >= 1, "Wrong number of arguments");
+
+  napi_valuetype valuetype0;
+  NAPI_CALL(env, napi_typeof(env, args[0], &valuetype0));
+
+  NAPI_ASSERT(env, valuetype0 == napi_number,
+    "Wrong type of arguments. Expects a number as first argument.");
+
+  int32_t input;
+  NAPI_CALL(env, napi_get_value_int32(env, args[0], &input));
+
+  napi_value output;
+  NAPI_CALL(env, napi_create_number(env, input, &output));
+
+  return output;
+}
+
 void Init(napi_env env, napi_value exports, napi_value module, void* priv) {
   napi_property_descriptor descriptors[] = {
     DECLARE_NAPI_PROPERTY("Test", Test),
+    DECLARE_NAPI_PROPERTY("TestInt32Truncation", TestInt32Truncation),
   };
 
   NAPI_CALL_RETURN_VOID(env, napi_define_properties(