Nov 20 2007

Test Driven Porting

Published by at 4:34 pm under .NET,Bell Ringing,Programming

Recently I’ve had reason to take an code library written in C++ and port it to C#.  Whilst I dabbled in C++ on a compilers course at university, I hated it then and I still hate it now.  I personally think it’s an abomination and should be consigned to the great garbage collector in the sky.   Whilst I can just about read the C++ syntax there is a lot that I don’t understand about it.

The library I was porting had semi reasonable documentation outlining what classes exist and their methods and a brief description of the overall usage.  This gave me a good starting point, however the documentation didn’t include example usages and expected results, for this I was forced to delve into the code.

One development paradigm I have been interested in but have been unable to find a decent project to test it on is Test-Driven-Development and this seemed like the perfect project to try it on.  So I set to work on the first iteration getting the test set up.   Without knowing exactly what results I should be expecting I was finding it hard going, so once again I dived back into the old code.

Thankfully, the developers of the C++ library had create a fairly comprehensive set of unit tests and with my limited C++ knowledge and a text editor with RegEx Find & Replace I was quickly able to convert their unit tests into NUnit based unit tests.

For example, what started out life as:

 1: void test_row_multiply_change(void)
 2: {
 3:  row r;
 4:  RINGING_TEST( ( r *= change( 6, "X" ) ) == "214365" );
 5:  RINGING_TEST( ( r *= change( 6, "1" ) ) == "241635" );
 6:  RINGING_TEST( ( r *= change( 8, "X" ) ) == "42615387" );
 7:  RINGING_TEST( ( r *= change( 5, "3" ) ) == "24651387" );
 8:  
 9:  RINGING_TEST( row( "214365" ) * change( 7, "5" ) == row( "1234675" ) );
 10: }

Quickly became:

 1: [Test]
 2: public void TestMultiplicationByChange()
 3: {
 4:  Row r = new Row();
 5:  Assert.AreEqual((Row)"214365", r *= new Change(6, "X") );
 6:  Assert.AreEqual((Row)"241635", r *= new Change(6, "1"));
 7:  Assert.AreEqual((Row)"42615387", r *= new Change(8, "X" ));
 8:  Assert.AreEqual((Row)"24651387", r *= new Change(5, "3"));
 9:  
 10:  Assert.AreEqual((Row)"1234675", new Row("214365") * new Change(7, "5"));
 11: }

Now, with a full set of unit tests at my disposal I was quickly able to bash away at the library and very quickly got working code without the need to trawl through ghastly C++ code.

Hooray for Test-Driven-Development and three cheers for Test-Driven-Porting.

ps. The library I’m porting is an open source library for Bell Ringing – yes I know I’m a geek but anyone that has followed everything else in this post must also be a geek ;-) .  Once I’m finished I will be releasing my code under an open source license as well, I just need to pick the right one.

pps. I may have exaggerated my hate of C++ a little.  I believe all languages have their place, even the esoteric languages like LOLCode.

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