Long post ahead, Summary: This post introduces a duck-typing extension
for JRuby, extending the possibilities for duck-typing involving java
classes. A working prototype is ready for download. Request for comments.
Hi all,
When testing java code (jruby, rspec), I frequently want to test code
that takes some argument that I want to mock. If the code looks like this
public void method1(ISomeInterface param) { ... }
everything is fine. If it looks like this
public void method2(AClassThatIsReallyHeavyToConstruct param) { ... }
I am in trouble. JRuby doesn't allow me to cloak my ruby classes as java
classes (duck-typing), only as java interfaces. Sometimes you can
inherit from the class that you want to mock, but as hinted at by the
example, this class is really to fat to construct and let's assume that
I can't.
So I hacked together a small prototype [3] that allows me to do exactly
that, using code I've found in jMock 2. The code allows you to
ruby_mock = flexmock(:some_mock) # or whatever
java_mock = DuckType::INSTANCE.transmogrify(ruby_mock,
AClassThatIsReallyHeavyToConstruct.java_class)
yielding a java class instance that looks exactly like a descendant of
AClassThatIsReallyHeavyToConstruct to the JVM, except that it's not. The
instance that you get is a proxy class instance that forwards all calls
to the ruby_mock object.
This obviously solves my problem and I can continue to test. But it is a
kludge; I would really like JRuby to do all this work for me. How about
merging this into JRuby? [1] This looks like a nice addition for the
java integration to me. [2]
I don't know the JRuby code base well enough to integrate this on my
own. I am working on it though - and perhaps someone might be willing to
help me with this?
kaspar
[1] Please disregard the bad state of the java code involved. Especially
that singleton-pattern is probably out of place. But I hope that you can
look at the essence and not at the form. (Which would have to be
changed in case of a JRuby integration)
[2] As far as possible, I've made sure that the original authors are
credited. I took the jMock ClassImpostorizer and special-purposed it. I
am also in contact with the author of the code - he is ok with this new
use.
[3] You can fetch the code from
http://absurd.li/system/posts/impostor.tgz. You'll need rspec and
possibly some other common stuff installed to be able to run the specs.
If you use this for your own projects, don't forget to include the .jars
in the ./lib dir.
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