Bubble emission testing is a traditional leak detection method that relies on visual observation. In this procedure, a sealed container is submerged in liquid and pressurized so that escaping gas forms visible bubbles. These bubbles indicate the presence and location of a leak. Although easy to perform, bubble testing has limited sensitivity and depends on operator interpretation. Because of these limitations, it is often used for basic demonstrations or preliminary testing. Modern pharmaceutical quality programs frequently combine bubble testing with more advanced deterministic methods for improved reliability.