There doesn’t seem to be an easy way to validate an XML document against a schema, so I figured I would roll my own library for it. Now, with that library, validating against a schema all of a sudden becomes easy. In the past, I hardly ever considered validating a document against a schema in my tests, but now I find myself doing it all over the place.

Anyway, I will just give a brief introduction. (And there really isn’t that much to talk about.)

First of all, let’s assume that you have a File reference to an XML file (xml) and a File reference to a RelaxNG schema file (schema). Now, in order to validate that file from JUnit, all you have to do is this:

assertThat(xml, isValidatedBy(schema));
That’s it. If all things are well, then you won’t see anything at all. However, if there is an error in your file, you might get something like this:
java.lang.AssertionError:
Expected: conforming to sample.rng
but: tag name "foo" is not allowed. Possible tag names are: <bar> at line <2>
In order to get these detailed messages (leveraging Hamcrest 1.2’s TypeSafeDiagnosingMatcher) from JUnit, you do however need to use MatcherAssert from Hamcrest itself. JUnit’s Assert class will not display the details.
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