Yes, there are several speed tests online. ATT has more than one. Try this one:
http://helpme.att.net/dsl/speedtest.
If you do not get better than half the speed advertised for your plan do call tech support.
Keep in mind you should not expect to get the max advertised speed when running the test. The test is "throughput" meaning it does not count the headers and other overhead. Also the advertised speed is the max speed within a range of speeds for the particular plan you subscribe to.
For example my plan advertises speeds "up to 3mb/s" I actually get a throughput of about 2.5mb/s. ATT tech sup told me that that plan only guarantees speed to be above 1.5 mb/s, which happens to be the max speed for the next lower plan.
Good luck.
Tony