Comment by avhon1

A large amount of the testing is performed by their proprietary test harness.

> TH3 consists of about 71.5 MB or 978.3 KSLOC of C code implementing 46622 distinct test cases. TH3 tests are heavily parameterized, though, so a full-coverage test runs about 1.9 million different test instances. The cases that provide 100% branch test coverage [of SQLite] constitute a subset of the total TH3 test suite. [1]

> SQLite itself is in the public domain and can be used for any purpose. But TH3 is proprietary and requires a license.

> Even though open-source users do not have direct access to TH3, all users of SQLite benefit from TH3 indirectly since each version of SQLite is validated running TH3 on multiple platforms (Linux, Windows, WinRT, Mac, OpenBSD) prior to release. So anyone using an official release of SQLite can deploy their application with the confidence of knowing that it has been tested using TH3. They simply cannot rerun those tests themselves without purchasing a TH3 license. [2]

[1] https://sqlite.org/testing.html

[2] https://sqlite.org/th3.html