Added multiple argument test to test/unit/math/prim/functor/apply_test.cpp

Author: bbbales2

test/unit/math/prim/functor/apply_test.cpp

@@ -85,3 +85,21 @@ TEST(MathFunctions, apply_temporary_function_return_const_reference) {
   EXPECT_EQ(1.0, y);
   EXPECT_TRUE((std::is_same<const double&, decltype(y)>::value));
 }
+
+TEST(MathFunctions, apply_two_args) {
+  std::tuple<double, int> x = std::make_tuple(1.5, 1);
+
+  auto y = stan::math::apply([](double x0, int x1) { return x0 + x1; }, x);
+
+  EXPECT_EQ(2.5, y);
+  EXPECT_TRUE((std::is_same<double, decltype(y)>::value));
+}
+
+TEST(MathFunctions, apply_three_args) {
+  std::tuple<double, double, int> x = std::make_tuple(1.5, 0.75, 1);
+
+  auto y = stan::math::apply([](double x0, double x1, int x2) { return x0 + x1 + x2; }, x);
+
+  EXPECT_EQ(3.25, y);
+  EXPECT_TRUE((std::is_same<double, decltype(y)>::value));
+}