[api] Add tests for Integer type

Since there is no `Value::IsInteger` method in the API, we in the
Node.js project are going to rely on what looks like an implementation
detail of the Integer class. It is currently possible to to call
`Integer::Value` on any Number and the value is cast to an integer.
This commit adds tests for this behavior.

Change-Id: I4de09e7c6e0beac7909e5477f7bfe2ed4c9415b9
Reviewed-on: https://chromium-review.googlesource.com/1200983
Commit-Queue: Michaël Zasso <mic.besace@gmail.com>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55629}

test/cctest/test-api.cc

@@ -5656,13 +5656,44 @@ THREADED_TEST(isNumberType) {
   obj = env->Global()->Get(env.local(), v8_str("obj")).ToLocalChecked();
   CHECK(obj->IsInt32());
   CHECK(obj->IsUint32());
-  // Positive zero
+  // Negative zero
   CompileRun("var obj = -0.0;");
   obj = env->Global()->Get(env.local(), v8_str("obj")).ToLocalChecked();
   CHECK(!obj->IsInt32());
   CHECK(!obj->IsUint32());
 }
 
+THREADED_TEST(IntegerType) {
+  LocalContext env;
+  v8::HandleScope scope(env->GetIsolate());
+  Local<Value> result;
+
+  // Small positive integer
+  result = CompileRun("42;");
+  CHECK(result->IsNumber());
+  CHECK_EQ(42, result.As<v8::Integer>()->Value());
+  // Small negative integer
+  result = CompileRun("-42;");
+  CHECK(result->IsNumber());
+  CHECK_EQ(-42, result.As<v8::Integer>()->Value());
+  // Positive non-int32 integer
+  result = CompileRun("1099511627776;");
+  CHECK(result->IsNumber());
+  CHECK_EQ(1099511627776, result.As<v8::Integer>()->Value());
+  // Negative non-int32 integer
+  result = CompileRun("-1099511627776;");
+  CHECK(result->IsNumber());
+  CHECK_EQ(-1099511627776, result.As<v8::Integer>()->Value());
+  // Positive non-integer
+  result = CompileRun("3.14;");
+  CHECK(result->IsNumber());
+  CHECK_EQ(3, result.As<v8::Integer>()->Value());
+  // Negative non-integer
+  result = CompileRun("-3.14;");
+  CHECK(result->IsNumber());
+  CHECK_EQ(-3, result.As<v8::Integer>()->Value());
+}
+
 static void CheckUncle(v8::Isolate* isolate, v8::TryCatch* try_catch) {
   CHECK(try_catch->HasCaught());
   String::Utf8Value str_value(isolate, try_catch->Exception());