Not necessarily solution. This is done as the granule often has better flow properties than the a fine powder and there is less de-mixing leading to better uniformity. The granules are then compressed to produce the tablet. The disintegration test may lead to an end point of tablet to granule only. The time is takes for the drug to dissolve from the dosage form.
Numerous factors affect dissolution.
Thus the dissolution medium, agitation, temperature are carefully controlled. The dissolution medium maybe water, simulated gastric juice, or 0.1M HCl. The U.S.P. methods are official however there is a wide variety of methods based on other apparatus. These are used because they may be faster, cheaper, easier, sensitive to a particular problem for a particular drug, or developed by a particular investigator. Dissolution tests are used as quality control to measure variability between batches which maybe be reflected by in vivo performance.