There is no definitive test for IC. The diagnosis is based on the presence of pain related to the bladder, usually accompanied by frequency and urgency of urine and in the absence of other diseases that could cause the symptoms.
In response to the pain, urgency and frequency the pelvic floor muscles and abdomen become tense going into a holding pattern. The tension becomes part of the problem further feeding into the holding patterns and pain cycle. The pelvic floor muscles need to be able to control at the neck of the bladder.
More about IC at www.ichelp.org