fix tests

Author: djeada

src/3_Stack_Queue/min_in_stack.cpp

@@ -28,9 +28,10 @@
  * of both the top element and the minimum element after a pop operation.
  */
 
+#include <algorithm>
+#include <cassert>
 #include <iostream>
 #include <optional>
-#include <cassert>
 #include <stack>
 #include <string>
 
@@ -54,13 +55,18 @@ template <typename T> class StackWithMin {
   }
 
   void pop() {
-    assert(!data_.empty());
+    if (data_.empty()) {
+      return;
+    }
     T top_val = data_.top();
     if (top_val < *min_value_) {
       // Restore the previous minimum.
       min_value_ = 2 * *min_value_ - top_val;
     }
     data_.pop();
+    if (data_.empty()) {
+      min_value_.reset();
+    }
   }
 
   std::optional<T> top() const {