A new twist on an old pattern for checking for exceptions

TestingIoFailure.java

@Test
public void ioFailure() throws Exception {
    final IOException ioFailure = new IOException("Simulating a failure writing to the file.");
    try {
        new WriteTextToFileActionImpl() {
            @Override
            protected FileWriter fileWriterOn(File path) throws IOException {
                return new FileWriter(path) {
                    @Override
                    public void write(String str, int off, int len) throws IOException {
                        throw ioFailure;
                    }
                };
            }
        }.writeTextToFile("::text::", new File("anyWritableFile.txt"));
        fail("How did you survive the I/O failure?!");
    } catch (IOException success) {
        if (success != ioFailure)
            throw success;
    }
}

Thank you for the tip on youDevise/matchers. I don't typically like to match on exception messages, because that makes the assertion hyperactive (fail too easily), but I see how not depending on the exception type/instance would provide a different dimension of freedom to change the code. It feels like a style choice to me, but only because I haven't tried it your way extensively yet.

Either way, I do like the running(...).throwsException(...) style. Thanks for that.

Glad I could help. I should probably admit that I wrote that particular matcher when I worked for youDevise, so I'm partial to it. I'm hoping that it'll make it into Hamcrest at some point.

If you want to match on messages but not worry about punctuation, etc. you can always provide a matcher to withTheMessage. For example: withTheMessage(containsString("failure")).

Thanks again. I just think in terms of regexes, so I naturally jump there first. (I know... now I have two problems.)