Add a unit test for tasks.c (#867)

* Add a unit test for tasks.c

This test simulates the scenario when a task with priority higher than
the currently executing task is unblocked as a result of the
xTaskIncrementTick call.

This is needed to fix the coverage drop in PR https://github.com/FreeRTOS/FreeRTOS-Kernel/pull/568.

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>

* Add description for the test

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>

* Add doc for another test

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>

FreeRTOS/Test/CMock/tasks/tasks_1_utest.c

@@ -2652,6 +2652,10 @@ void test_xTaskIncrementTick_success_update_next_unblock( void )
     TEST_ASSERT_EQUAL( xTickCount + 4, xNextTaskUnblockTime );
 }
 
+/* Tests the scenario when a task with priority equal to the
+ * currently executing task is unblocked as a result of the
+ * xTaskIncrementTick call. Also, xPendedTicks is set to
+ * non-zero to ensure that tick hook is not called. */
 void test_xTaskIncrementTick_success_unblock_tasks( void )
 {
     BaseType_t ret_task_incrementtick;
@@ -2693,6 +2697,10 @@ void test_xTaskIncrementTick_success_unblock_tasks( void )
     TEST_ASSERT_EQUAL( portMAX_DELAY, xNextTaskUnblockTime );
 }
 
+/* Tests the scenario when a task with priority equal to the
+ * currently executing task is unblocked as a result of the
+ * xTaskIncrementTick call. Also, xPendedTicks is set to 0 to
+ * ensure that tick hook is called. */
 void test_xTaskIncrementTick_success_unblock_tasks2( void )
 {
     BaseType_t ret_task_incrementtick;
@@ -2735,6 +2743,49 @@ void test_xTaskIncrementTick_success_unblock_tasks2( void )
     ASSERT_APP_TICK_HOOK_CALLED();
     TEST_ASSERT_EQUAL( portMAX_DELAY, xNextTaskUnblockTime );
 }
+
+/* Tests the scenario when a task with priority higher than the
+ * currently executing task is unblocked as a result of the
+ * xTaskIncrementTick call. Also, xPendedTicks is set to
+ * non-zero to ensure that tick hook is not called. */
+void test_xTaskIncrementTick_success_unblock_tasks3( void )
+{
+    BaseType_t ret_task_incrementtick;
+    TaskHandle_t task_handle;
+
+    /* Setup. */
+    create_task_priority = 4;
+    task_handle = create_task();
+    block_task( task_handle );
+    create_task_priority = 3;
+    ( void ) create_task();
+    ptcb = task_handle;
+    xPendedTicks = 3;
+    xTickCount = 50;
+    xNextTaskUnblockTime = 49; /* Task 2 is due unblocking. */
+    uxSchedulerSuspended = pdFALSE;
+
+    /* Expectations. */
+    listLIST_IS_EMPTY_ExpectAndReturn( pxDelayedTaskList, pdFALSE );
+    listGET_OWNER_OF_HEAD_ENTRY_ExpectAndReturn( pxDelayedTaskList, task_handle );
+    listGET_LIST_ITEM_VALUE_ExpectAndReturn( &task_handle->xStateListItem,
+                                             xTickCount - 5 );
+    listREMOVE_ITEM_Expect( &( task_handle->xStateListItem ) );
+    listLIST_ITEM_CONTAINER_ExpectAndReturn( &task_handle->xEventListItem, NULL );
+    listINSERT_END_Expect( &pxReadyTasksLists[ task_handle->uxPriority ],
+                           &task_handle->xStateListItem );
+    listLIST_IS_EMPTY_ExpectAndReturn( pxDelayedTaskList, pdTRUE );
+    listCURRENT_LIST_LENGTH_ExpectAndReturn( &pxReadyTasksLists[ task_handle->uxPriority ], 1 );
+
+    /* API Call */
+    ret_task_incrementtick = xTaskIncrementTick();
+
+    /* Validations */
+    TEST_ASSERT_EQUAL( pdTRUE, ret_task_incrementtick );
+    ASSERT_APP_TICK_HOOK_NOT_CALLED();
+    TEST_ASSERT_EQUAL( portMAX_DELAY, xNextTaskUnblockTime );
+}
+
 /* testing INCLUDE_xTaskAbortDelay */
 void test_xTaskAbortDelay_fail_current_task( void )
 {