This project is a test generator for type checkers such as Flow. It generates programs with runtime checks, feeds them to a type checker and runs those programs to see if the type checker will reject bad programs.

To build the executable, run make.

ruleset_base.ml contains a lot of rules used to generate programs. However, to accomplish a certain task, one might not want to use all those rules. Instead, a recommended way to do that is to inherit the ruleset_base class, pick the necessary rules and possibly overwrite those methods.

Here are the steps to extend the base ruleset and ruleset_optional.ml, ruleset_func.ml, ruleset_depth.ml, ruleset_union.ml and ruleset_exact.ml serve as examples for this extension:

1. Suppose you want to test exact object types and want to generate some programs related to exact object types. (ruleset_exact.ml has all the code)
2. Copy one of the children class of base ruleset, say, ruleset_depth.ml to ruleset_exact.ml. Make classname adjustments in there appropriately.
3. Modify the build file
4. Then, in codegen.ml, add ruleset_exact as one of the engines
5. Compile the program and run

In the folder where binary lives, run the program once to let it generate an initial config file called flowtestgen.json. Then edit flowtestgen.json to up the number of trials (num_prog). The typecheck flag controls whether Flow is invoked or not. Log_to_console controls prints programs to console.

To try random searching, each ruleset has a random version of that class as well at the bottom of the file.