more stack tests and fix in stack

stack.c

@@ -50,6 +50,8 @@ void *top(StackNode *stack)
 // Clears stack and releases all memory.
 void clearStack(StackNode *stack)
 {
-    while (pop(stack))
-        ;
+    while (stack)
+    {
+        stack = pop(stack);
+    }
 }

test_stack.c

@@ -15,6 +15,7 @@ void setUp(void)
 void tearDown(void)
 {
     clearStack(stack);
+    stack = NULL;
 }
 
 void test_push_and_pop(void)
@@ -31,17 +32,33 @@ void test_push_and_pop(void)
     stack = pop(stack);
 }
 
+// pop and top should return NULL if called with NULL ptr
 void test_handle_NULL(void)
 {
     TEST_ASSERT_NULL(pop(stack));
     TEST_ASSERT_NULL(top(stack));
 }
 
+void test_top(void)
+{
+    TEST_ASSERT_NULL(top(stack));
+    stack = push(stack, &data1);
+    TEST_ASSERT_EQUAL_PTR(top(stack), &data1);
+    TEST_ASSERT_EQUAL_INT(*(int *)top(stack), data1);
+    stack = push(stack, &data2);
+    TEST_ASSERT_EQUAL_PTR(top(stack), &data2);
+    TEST_ASSERT_EQUAL_INT(*(int *)top(stack), data2);
+    stack = push(stack, &data3);
+    TEST_ASSERT_EQUAL_PTR(top(stack), &data3);
+    TEST_ASSERT_EQUAL_INT(*(int *)top(stack), data3);
+}
+
 int main(void)
 {
     printf("============================\nStack tests\n============================\n");
     UNITY_BEGIN();
     RUN_TEST(test_push_and_pop);
     RUN_TEST(test_handle_NULL);
+    RUN_TEST(test_top);
     return UNITY_END();
 }