Test driven development - when/what to test?

nfl2000

I am trying to get started with TDD but right away I am unsure of when and what I should be testing. The first two tasks in a new project I'm working on are as follows -

1) Create a REST endpoint that receives some JSON formatted data on a saves it to the database. Say the data was several car records -

{
    "cars": [{
            "make": "ford",
            "color": "blue",
            "year": "2010",
            "for_sale": true
        }, {
            "make": "bmw",
            "color": "black",
            "year": "2011",
            "for_sale": false
        }
    ]
}

So that data arrives at a REST endpoint and I need to save it in the database. Do I need a test (or a number of tests) for this task and if so what should it look like? How should I approach the job of testing this task, do I write out a list of things that should be tested...if so, what would such a list look like?

2) Retrieve some records from the database and display them in a view/webpage (i.e. using some templating system). Say the records are the car records above and they should be displayed as follows -

[HTML]<ul id="cars">
<li id="car-1">
<div><span>Make:</span><span>Ford</span>
</div>
<div><span>Color:</span><span>blue</span>
</div>
<div><span>Year:</span><span>2010</span>
</div>
<div><span>For sale:</span><span>Yes</span>
</div>
</li>
<li id="car-2">
<div><span>Make:</span><span>BMW</span>
</div>
<div><span>Color:</span><span>black</span>
</div>
<div><span>Year:</span><span>2011</span>
</div>
<div><span>For sale:</span><span>No</span>
</div>
</li>
</ul>[/HTML]

So do I need a test for this task and if so what should it look like?

John_Mc

The 3 scenarios are:

1) It fails
2) It succeeds
3) There's an exception

With TDD you need to know the inputs and the desired outputs. In this case, the output is a call to the data access layer to add your record.

In the second method, you are testing that the DAL returns records for the given parameters.

Your tests for handling failures and exceptions should be testing the scenarios where something wrong has happened. Like input parameters being empty or in the incorrect format.

stevenmu

You should read up a bit about unit testing, which in very very shorthand is really just creating tests for individual units of functionality in your project.

For the first task, you need to create a unit test that can call an your REST endpoint, passing in the JSON data. Either this test will also test that the data makes it through to the DB, or it will just the response from the endpoint and you would write another test to check that it goes through to the DB ok.

Then when your unit tests are ready, you write the code for your REST endpoint to pass the unit tests.

John_Mc

If you're using .Net and Visual Studio then I'd suggest installing the trial version of NCrunch.

It's a Unit Test runner which graphically displays the lines covered and not covered by your unit tests. Very helpful and should give you a boost with the learning curve as it runs the tests each time they are changed (without you having to tell Visual studio to compile and run them).