A recently drilled appraisal well in a multilayered carbonate reservoir was successfully tested using downhole tools in very hostile downhole conditions. While the reservoir pressure and temperature were not excessive, the combined concentrations of hydrogen sulfide (H2S) and carbon dioxide (CO2) were well above anything that has been tested in the past with similar tools. Four different zones were tested individually using a fit-for-purpose test design, which allowed for testing two zones per trip. The services included downhole tools for shut-in and well-control purposes, bottomhole samplers, memory gauges, through-tubing perforating and coiled-tubing intervention through the test string to acid stimulate, N2 lift, and set cement plugs between zones. The use of the downhole test string provided the means to carry out a complete well test with downhole shut-in and sampling controlled from the surface. The operational flexibility offered by the string allowed for all operations to be successfully performed even with lengthy exposures of the tools to sour fluids. This appraisal well is one of a series of wells drilled in this area but the first one in which very extensive data acquisition has been acquired thanks to a detailed well-test procedure and job planning. This test required a significant amount of prejob planning, in addition to attention to detail in the execution and onsite preparation and maintenance. Our paper describes the test requirements, the prejob planning, and the execution that led to the successful completion of this well test in very hostile conditions, the first of its kind in this part of the world.