Online tests are no replacement for a consultation with a good specialist, but they can act as benchmarks so we can go back and take the test at a later point and compare the two results. They can also shock you into making an appointment with a specialist in the first place, if that’s appropriate for your situation.
Here is a screening test for depression. I’ve gone over it and it indeed does appear to be confidential, free, and the results are roughly accurate in that they agree with most professionally accepted definitions of the various stages of depression. The test is not exhaustive, but it is detailed enough to be useful, so take it for what it’s worth. The website apparently derives its money from referrals to specific practitioners, but just don’t bother clicking on referrals: ask your own doctor for one instead.
To use this on your blog, I would suggest you copy the entire result page and post it, password-protecting it. Then only those you give the password to will be able to read it. Having it somewhere external to yourself means that you can refer to it a month, or a year later and see how far you’ve come, and it makes it seem more real somehow. You could even re-take the test again if you want to track your progress. But password protecting it is probably a good idea, particularly if you blog under your real name.