I took many tests like this via Project Implicit online. I'm not sure the results are very reliable for individuals, though that is not to say they are unreliable on average.
For instance, I took a racism test in demonstration mode. I was anxious about the exam as I took it, and in particular I was distracted because I had figured out how it worked and I was self-conscious about making "mistakes" (responding more quickly in some scenarios by fluke) or sort-of secretly biasing the result because I didn't want myself to be racist. In the end it told me I had a moderate automatic preference for whites over blacks. Although I do not consider myself racist, I was willing to accept this because I grew up in the Midwest with many racist peers and over the course of my life have had very little exposure to black people.
But then I encountered the same test as part of the experimental section of the site. This time I was much more relaxed because I had come to terms with the previous results. Yet, after this test, it told me I had no automatic preference for whites or blacks.
I don't know whether my performance during the first test was skewed because I was anxious and distracted, whether my second test was skewed because I had taken the test before, or whether there is some large uncertainty and my "true" score is simply between these. I also don't know if my seeing how the experiment works -- and then being distracted by it -- is common or rare.