TSTL is a domain-specific language (DSL) and set of tools to support automated generation of tests for software. This implementation targets Python. You define (in Python) a set of components used to build up a test, and any properties you want to hold for the tested system, and TSTL generates tests for your system. TSTL supports test replay, test reduction, and code coverage analysis, and includes push-button support for some sophisticated test-generation methods. In other words, TSTL is a property-based testing tool. TSTL has been used to find and fix real faults in real code, including ESRI's ArcPy (http://desktop.arcgis.com/en/arcmap/latest/analyze/arcpy/what-is-arcpy-.htm), sortedcontainers (https://github.com/grantjenks/sorted_containers), gmpy2 (https://github.com/aleaxit/gmpy), sympy (http://www.sympy.org/en/index.html), pyfakefs (https://github.com/jmcgeheeiv/pyfakefs), Python itself (https://bugs.python.org/issue27870), the Solidity compiler (https://github.com/ethereum/solidity), a Solidity static analysis tool, and even OS X.