The Sybase QuaSR project manages thousands of automated tests for Sybase Inc's. SQL RDMS, each implemented as an independent Tcl program. The resulting test suite, significantly more than a million lines of code, comprises the largest known Tcl code base. The test harness is written in incr Tcl and the test cases in Tcl. Tcl and incr Tcl's extensibility, simplicity, and reliability have made them uniquely suited to the development of a sophisticated automated testing system.
As indicated by this presentation by Sudipta Chatterjee, QuaSR is still going strong in 2012.