When running JS tests via compilerJs::TestRunner I believe there's a problem on line 220 which essentially says:

return engine.eval( ... ) -> toInt

Only eval() returns a java.lang.Integer and not a sys::Int so there is no toInt() method to invoke, raising the error:

sys::UnknownSlotErr: [java]java.lang::Integer.toInt
  fan.sys.JavaType.slot (JavaType.java:113)
  fan.sys.FanObj.doTrap (FanObj.java:187)
  fan.sys.FanObj.trap (FanObj.java:179)
  compilerJs::TestRunner.runTest (TestRunner.fan:220)
  compilerJs::TestRunner.runTests (TestRunner.fan:141)
  fan.sys.List.each (List.java:588)
  compilerJs::TestRunner.runTests (TestRunner.fan:138)
  compilerJs::TestRunner.main (TestRunner.fan:65)
  fan.sys.List.each (List.java:588)
  compilerJs::TestRunner.main (TestRunner.fan:65)
  ...

Note this error causes ALL the tests to fail.

fant has been migrated to use Node.js as the underlying platform for running javascript tests instead of using the built-in Java JS engine (rhino/nashorn).

compilerJs::TestRunner should be considered deprecated for 1.0.70, and it will be removed in 1.0.71. If you want to run javascript tests using "raw" fantom invocation, use

fan compilerJs::NodeRunner

NodeRunner
Usage:
  NodeRunner [options] -test <pod>[::<test>[.<method>]]
  NodeRunner [options] -run <script>
Options:
  -keep      Keep intermediate test scripts