It depends on what you are testing for integrity.
If you are looking for a whole-package integrity test, then you want to explore the bubble leak route via ASTM F2096 Standard Test Method for Detecting Gross Leaks in Packaging by Internal Pressurization (Bubble Test). A package is inflated to a determined minimum test pressure and held under water for 5 seconds while the operator rotates the package around inspecting for any defects. This is a good way to find failures such as pin holes, cracks, tears, or anything associated with the whole-package.
If you are looking for a seal integrity test, then you will want to look towards visual inspection via ASTM F1886 Standard Test Method for Determining Integrity of Seals for Flexible Packaging by Visual Inspection or at the dye leak test per ASTM F1929 Standard Test Method for Detecting Seal Leaks in Porous Medical Packaging by Dye Penetration. These tests look specifically at the seal to see if there are any imperfections giving way to contamination.
Whatever kind of integrity testing you are looking for it is important to understand the relationship between the package and product. If you are validating the packaging system and its ability to make it through the distribution cycle while maintaining a sterile barrier, then whole-package integrity testing is the way to go. If you are trying to validate a piece of equipment or the closure seal that is created then Dye leak testing for the seal integrity would be the path to choose.