Add void_cast test

Author: lucic71

tests/unit/void_cast.cpp

@@ -0,0 +1,74 @@
+#include <cassert>
+
+void unused_param(int x) { (void)x; }
+
+int side_effect_counter = 0;
+int bump_and_return() {
+  ++side_effect_counter;
+  return side_effect_counter;
+}
+
+struct Holder {
+  int field;
+};
+
+int main() {
+  unused_param(42);
+
+  int y = 5;
+  (void)y;
+
+  int z = ((void)y, 7);
+  assert(z == 7);
+
+  int counter = 0;
+  int w = ((void)counter, counter = 3, counter);
+  assert(w == 3);
+  assert(counter == 3);
+
+  (void)bump_and_return();
+  assert(side_effect_counter == 1);
+
+  int v = ((void)bump_and_return(), 99);
+  assert(side_effect_counter == 2);
+  assert(v == 99);
+
+  (void)0;
+  (void)(0);
+
+  (void)(y);
+
+  ((void)0);
+  ((void)(y));
+
+  int err = 0;
+  ((void)(err = 42));
+  assert(err == 42);
+
+  int chosen = ((void)(err = 7), 123);
+  assert(err == 7);
+  assert(chosen == 123);
+
+  (void)bump_and_return;
+  assert(side_effect_counter == 2);
+
+  (void)(&bump_and_return);
+  assert(side_effect_counter == 2);
+
+  (void)(static_cast<int (*)()>(&bump_and_return));
+  assert(side_effect_counter == 2);
+
+  int storage = 11;
+  int *p = &storage;
+  (void)(*p);
+
+  int arr[] = {1, 2, 3};
+  (void)(arr[1]);
+
+  Holder h{17};
+  (void)(h.field);
+  Holder *hp = &h;
+  (void)(hp->field);
+
+  return 0;
+}