...same for the invoice lines - great, everything's working!✅
I hear you say: "But, Jan, you could have also written the implementation first and then the test - it doesn't really matter, does it!?" - Hold On! We are actually not done yet with our implementation of the requirements! Besides posting and displaying the _real_ invoice, there is often the concept of a so-called "proforma" invoice, which essentially is a "draft" invoice, which is not actually posted and has no invoice number.
2/?
...same for the invoice lines - great, everything's working!✅
I hear you say: "But, Jan, you could have also written the implementation first and then the test - it doesn't really matter, does it!?" - Hold On! We are actually not done yet with our implementation of the requirements! Besides posting and displaying the _real_ invoice, there is often the concept of a so-called "proforma" invoice, which essentially is a "draft" invoice, which is not actually posted and has no invoice number.
2/?
What's to highlight here is that the data sources from which to retrieve the data for the proforma variant are actually _different_ from the ones used for the real invoice. So we need to test and implement this as well!
While we're setting up the test for the proforma invoice (remember: we are doing #TDD!), I'd like to remind you of the first sentence in this thread: we are dealing with a _legacy_ system here: setting up the test is often way more work than doing the actual implementation!
3/?
And the API for posting the invoice is... not great! It goes something like:
invoicePoster.initParams(/* pass in six or so arguments! */);
invoicePoster.queryLines(true);
invoicePoster.callerRecord(foo);
invoicePoster.proforma(true);
invoicePoster.post();
Why do I tell you all this!? Well, this has given me time to implement the actual "proforma" test by now! 🙂
Great, let's execute our proforma test...
4/?
aaaand...it _passes_!?✅ Wait, why is that? It should have failed! I told you that different data sources are accessed depending on whether it's a real or proforma invoice, remember!? So something's fishy here! I've also shown you the code on how to post a (proforma) invoice... except that line 2 and 3 should have been swapped! 🙃 - otherwise it doesn't generate the proforma invoice, but posts the _real_ invoice!
5/?
If we hadn't done TDD here, we would have believed that we are testing the proforma invoice when it fact we hadn't! TDD has saved us from implementing a buggy test (and potentially a buggy implementation)!
So do TDD! It is a very useful software engineering discipline!
#SoftwareDevelopment #Quality #Testing
6/6
@janriemer
I am also a bigfan of TDD, sadly most companies who hire me for contracts use the "we do not have time for this" excuse, even if i show them that it saves time/money in the long run.
Luckily some even pay for TDD development.
