Add destroy def and unit test

test/controllers/api/v1/tasks_controller_test.rb

@@ -75,4 +75,22 @@ class Api::V1::TasksControllerTest < ActionDispatch::IntegrationTest
     as: :json
     assert_response :forbidden
   end
+
+  # DESTROY
+  test "should destroy task" do
+    assert_difference "Task.count", -1 do
+    delete api_v1_activity_task_url(@activity, @task),
+    headers: { Authorization: JsonWebToken.encode(user_id: @user.id) },
+    as: :json
+    end
+    assert_response :no_content
+  end
+
+  test "should not destroy task" do
+    assert_no_difference('Task.count') do
+    delete api_v1_activity_task_url(@activity, @task),
+    as: :json
+    end
+    assert_response :forbidden
+  end
 end