Object Mentor Blog: The Polyglot Tester

The Polyglot Tester

Uncle Bob — Sat, 19 Dec 2009 11:22:00 -0600

Behavior Driven Development, and it’s emphasis on the Given / When / Then structure of specification has been well accepted by many parts of the software industry. Tools such as JBehave, Cucumber, GivWenZen, have taken a prominent role, and rightly so. After all, it’s hard to argue with the elegance of simple statements such as:

Given that I am a user named Bob with password xyzzy
When I log in with username Bob and password xyzzy
Then I should see “Welcome Bob, you have logged in”.

Yes, it’s hard to argue with it, but argue I shall…

The BDD style is very pretty. Certainly business people can easily read and write it. Moreover, the BDD style provides a conceptual framework within which automated test specification and be efficiently composed. Better still, the BDD tools provide a powerful parsing mechanism that conveniently translates the natural GWT statements into function calls to be executed as tests.

The problem is that the BDD style is simply not appropriate for all, or even most kinds of tests. Why? Because it’s wordy. Consider:

Given a Juke box that shows 0 credits
When I deposit .25
Then the Juke Box shows 1 credit.

Given a Juke box that shows 0 credits.
When I deposit 1.00
Then the Juke Box shows 5 credits.

Given a Juke Box that shows 0 credits.
When I deposit 5.00
Then the Juke Box shows 30 credits.

How is this better than:

Jukebox Credit Table

Deposit	Credits
25	1
1.00	5
5.00	30

Which of the two is the more elegant?
Which of the two is easier to read?
If you were looking for a specification error, in which of the two would you be more likely to find it?

I think the answers are rather obvious.

There is value in brevity.
There is elegance in sparseness.
Elaborate wordy structures are not always the best approach.

OK, I can hear the complaints starting to bubble up already; so hold on. I’m not arguing against BDD. I really like the GWT style. And Yes, I realize that many of the BDD testing tools allow you to compress your tests into tables so that you can avoid the wordiness.

My issue is not with the tools. My issue is with the idea that BDD is the only true way, and that all tests should be expressed in GWT format forever and ever amen.

Is this a strawman? Unfortunately not. In my travels over the last several years, I have seen this attitude showing up over and over again. Someone will write a suite of complex tests using GWT style, without realizing that they could shorten it by a factor of 10 or so by recomposing it into a simple table.

Actually my issue is with the tools. Cucumber, for example, is written around Given, When, Then. If you use Cucumber, or JBehave, or any of the other BDD tools, you think in GWT and find it hard to even express something as simple as the table above.

Consider, for example, the following strange test. It measures how well the juke box selects random songs based upon their popularity. More popular songs should be played more often than less popular songs. You might specify it this way in GWT style.

Given a Juke box with 1 credit
When the user presses “You Decide”
Then the juke box will randomly choose a song based on its ranking.

Now this is a perfectly good statement of intent, and I’d certainly want it to turn green if I ran the test. However, if this turns green, what have we really learned? The test result does not really tell us whether or not the selection algorithm is accurate. The GWT statements above are really just hand-waving statements that loudly say Trust Me without necessarily verifying anything.

Now look at the following tables.

Repeat you decide 10000 times and count results

Average credits should ~=1.3

Song	Times played
Stairway to Heaven	880 < _ < 1120
In-a-godda-da-vida	1880 < _ < 2120
Viva La Vida	2880 < _ < 3120
Incense and Peppermint	880 < _ < 1120
Comfortably Numb	2880 < _ < 3120

Perhaps you don’t like the magic numbers. There are ways to deal with that, but they are beyond the scope of this blog. So let’s forget about the magic-ness of the numbers for the moment. When you run this test you see something like this:

Repeat you decide 10000 times and count results

Average credits should 1.295 ~=1.3

Song	Times played
Stairway to Heaven	880 < 998 < 1120
In-a-godda-da-vida	1880 < 2007 < 2120
Viva La Vida	2880 < 2950 < 3120
Incense and Peppermint	880 < 1019 < 1120
Comfortably Numb	2880 < 3026 < 3120

It’s hard to argue that the green-ness is hand-waving. Nothing here says: Trust Me. You can see that the selection algorithm is random, and is weighted properly.

Now I’m certain that we could construct a set of GWT statements that captures the above semantics perfectly; but why would we? The simple tables express the intent in a format that is simpler and more accessible than GWT.

Conclusion

As programmers we have already learned that we must be polyglots. If you want to write a rails system you’d better know ruby, haml, css, erb, xml, etc. If you want to write a J2EE system, you’d better know Java, JSP, HTML, XML, CSS, etc.

Testers also need to be polyglots. Writing in a single style such as GWT is not going to cut it. GWT has it’s place, but it’s not sufficient. Other testing languages are also useful. Therefore testing tools need to be polyglot tools.

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