Importance of Unit tests — My journey with Unit-tests 2

I will list my own recent experiences learning C++ data-structures with Unit-tests (using googletest framework) in this post.

For the beginning, I started with Single Linked-Lists with C++. My approach was to write a unit test and the go for the development of that feature, not pure TDD.

1. Identify bugs earlier

In my code-base I tried to add a new node to the list. Following is my code.

#include <cstddef>

class LinkedList{
  public:
    int value {0};
    LinkedList* nextNode {NULL};
};

LinkedList* addNewNode(int nodeVal){

  LinkedList *newNode;
  newNode->value = nodeVal;
  newNode->nextNode = nullptr;

  return newNode;
}

Unit test for this feature :

TEST_F(LinkedListTest,addNewNodeReturnsItsNodePointer){
    linkedlist = addNewNode(5);

    EXPECT_TRUE(linkedlist != nullptr);
    ASSERT_EQ(linkedlist->value,5);
    EXPECT_TRUE(linkedlist->nextNode != nullptr);
}

When I execute the unit test, I got

Segmentation fault

I tried to sort this thing out my self, but couldn't and finally end-up in stackoverflow. As answer suggested, I forgot to initialize newNode . But this unit test failure helped me to identify the possible bug.

2 . Identify problems in logic

In next part, I was trying to get the node with the given value in that node. I successfully completed the part when the given value is in the list. But when I wanted to test the failure cases for this logic, I got stuck again.

LinkedList* getANodeWithGivenValue(LinkedList *existingList,int value){
   while (existingList != NULL){
      if(existingList->value == value){
          return existingList;
      }
      existingList = existingList->nextNode;
   }
}

With this logic, unit test kept failing.

TEST_F(LinkedListTest,getANodeWithGivenValueNoMatchingValueReturnsFalse){
    LinkedList *existingList = addNewNode(1);
    LinkedList *nodeWithTheGivenValue =     getANodeWithGivenValue(existingList,5);
    EXPECT_TRUE(nodeWithTheGivenValue->nextNode == nullptr);
    EXPECT_EQ(nodeWithTheGivenValue->value,0);
}

My expectation was that if `getANodeWithGivenValue` function does not match anything, it will automatically goes to empty node value. My ego was saying that my logic is right, there is an issue in the unit-test.

Finally I understood my issue, `getANodeWithGivenValue` is having an issue for a value not in the list. It just returns the list after finishing while loop.

This is a short post regarding my issues. Not a well constructed post.