MDD meets TDD (part II): Code Generation

Here at Abstratt we are big believers of model-driven development and automated testing. I wrote here a couple of months ago about how one could represent requirements as test cases for executable models, or test-driven modeling. But another very interesting interaction between the model-driven and test-driven approaches is test-driven code generation.

You may have seen our plan for testing code generation before. We are glad to report that that plan has materialized and code generation tests are now supported in AlphaSimple. Follow the steps below for a quick tour over this cool new feature!

Create a project in AlphaSimple

First, you will need a model so you can generate code from. Create a project in AlphaSimple and a simple model.

package person;

enumeration Gender 
  Male, Female

class Person
    attribute name : String; 
    attribute gender : Gender; 


Enable code generation and automated testing

Create a file in your project to set it up for code generation and automated testing:

# declares the code generation engine

# imports existing POJO generation template projects

# declares a code generation test suite in the project

# enables automated tests (model and templates)

Write a code generation test suite

A code generation test suite has the form of a template group file (extension .stg) configured as a test template (already done in the above).

Create a template group file named my_tests.stg (because that is the name we declared in, with the following contents:

group my_tests : pojo_struct;

actual_pojo_enumeration(element, elementName = "person::Gender") ::= "<element:pojoEnumeration()>"

expected_pojo_enumeration() ::= <<
enum Gender {
    Male, Female

A code generation test case is defined as a pair of templates: one that produces the expected contents, and another that produces the actual contents. Their names must be expected_<name> and actual_<name>. That pair of templates in the test suite above form a test case named “pojo_enumeration”, which unsurprisingly exercises generation of enumerations in Java. pojo_enumeration is a pre-existing template defined in the “Codegen – POJO templates” project, and that is why we have a couple of projects imported in the file, and that is why we declare our template suite as an extension of the pojo_struct template group. In the typical scenario, though, you may would have the templates being tested and the template tests in the same project.

Fix the test failures

If you followed the instructions up to here, you should be seeing a build error like this:

Line	File		Description
3	my_tests.stg	Test "pojo_enumeration" failed: [-public -]enum Gender {n Male, Femalen}

which is reporting the code generated is not exactly what was expected – the template generated the enumeration with an explicit public modifier, and your test case did not expect that. Turns out that in this case, the generated code is correct, and the test case is actually incorrect. Fix that by ensuring the expected contents also have the public modifier (note that spaces, newlines and tabs are significant and can cause a test to fail). Save and notice how the build failure goes away.

That is it!

That simple. We built this feature because otherwise crafting templates that can generate code from executable models is really hard to get right. We live by it, and hope you like it too. That is how we got the spanking new version of the POJO target platform to work (see post describing it and the actual project) – we actually wrote the test cases first before writing the templates, and wrote new test cases whenever we found a bug – in the true spirit of test-driven code generation.

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2 thoughts on “MDD meets TDD (part II): Code Generation

  1. Ken Lyle

    November 7, 2011 at 4:42pm

    Hey Rafael, Thanks for this.

    So, is “No tests found for my_tests” the “correct” answer, at the end of this exercise?

  2. rafael.chaves

    November 7, 2011 at 8:41pm

    Hmm, that would suggest your actual_ and expected_ templates don’t have the same suffix (like “actual_pojo_enumeration” and expected_pojo_enumeration”).

    I just went through this and go stuck as well, but with a different error:

    Internal error (java.lang.IllegalArgumentException: Can't find template; context is [actual_pojo_enumeration]; group hierarchy is [my_tests])

    but that was because I forgot to declare the template ancestor:

    group my_tests : pojo_struct;

    Please make sure your template starts with that. I just updated the example code for the template accordingly.

    The final goal of the exercise is to produce no errors, IOW, something like this:

    Model compiled successfuly in 0.147s
    Code generation tested successfuly in 0.51s

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