Methods of draw-down and build-up testing on existing production wells are disclosed. The testing may be accomplished without removing the production tubing string from the well. The production of the well is shut down and then a coiled tubing test string is run down into the production tubing string. The coiled tubing test string includes a coiled tubing string, a tester valve carried by the coiled tubing string, and a test packer carried by the coiled tubing string. The test packer is set within one of the casing bore and the production tubing bore above perforations which communicate the casing bore with a subsurface formation. Draw-down and build-up testing of the subsurface formation can then be accomplished by opening and closing the tester valve to selectively flow well fluid up through the coiled tubing string or shut in the coiled tubing string. After the draw-down/build-up testing is completed, the coiled tubing test string is removed from the well and production of the well is resumed up through the production tubing bore of the production tubing string. Optionally, the coiled tubing test string may carry a perforating gun to perforate a new zone of the well which may then be tested.