Unable to run unittest that contain ValidationRules

Start with src/app.ts and the updated spec in the linked reproduction repository, then run au test to reproduce the ValidationRules failure. Trace the reported call into aurelia-validation.js and compare the test setup with the application setup. Done means the component test runs without the accessor parsing exception.

I'm submitting a bug report

• Library Version:
  1.0.0

Please tell us about your environment:

• Operating System:
  Windows 10

• Node Version:
  V10.16.0

• NPM Version:
  6.9.0

• JSPM OR Webpack AND Version
  webpack 4.34.0

• Browser:
  n/a

• Language:
  TypeScript 3.1.2

Current behavior:
When running a test that tests a component which uses ValidationRules, the following error pops up:

    ------------------------------------------------
    Inner Error:
    Message: Unable to parse accessor function:
    function (a) {
          /* istanbul ignore next */
          cov_q8rv1u7dl.f[2]++;
          cov_q8rv1u7dl.s[5]++;
          return a.message;
        }
    Inner Error Stack:
    Error: Unable to parse accessor function:
    function (a) {
          /* istanbul ignore next */
          cov_q8rv1u7dl.f[2]++;
          cov_q8rv1u7dl.s[5]++;
          return a.message;
        }

      at getAccessorExpression (node_modules/aurelia-validation/dist/commonjs/aurelia-validation.js:113:15)
      at PropertyAccessorParser.Object.<anonymous>.PropertyAccessorParser.parse (node_modules/aurelia-validation/dist/commonjs/aurelia-validation.js:95:28)
      at FluentEnsure.Object.<anonymous>.FluentEnsure.ensure (node_modules/aurelia-validation/dist/commonjs/aurelia-validation.js:1703:42)
      at Function.Object.<anonymous>.ValidationRules.ensure (node_modules/aurelia-validation/dist/commonjs/aurelia-validation.js:1770:58)
      at new App (src/app.ts:219:42)
      at Object.invoke (node_modules/aurelia-dependency-injection/dist/commonjs/aurelia-dependency-injection.js:379:24)
      at InvocationHandler.Object.<anonymous>.InvocationHandler.invoke (node_modules/aurelia-dependency-injection/dist/commonjs/aurelia-dependency-injection.js:352:28)
      at Container.Object.<anonymous>.Container.invoke (node_modules/aurelia-dependency-injection/dist/commonjs/aurelia-dependency-injection.js:538:28)
      at ProviderResolver.get (node_modules/aurelia-templating/dist/commonjs/aurelia-templating.js:2305:72)
      at Container.Object.<anonymous>.Container.get (node_modules/aurelia-dependency-injection/dist/commonjs/aurelia-dependency-injection.js:493:28)
      End Inner Error Stack
      ------------------------------------------------
      at new AggregateError (node_modules/aurelia-pal/dist/commonjs/aurelia-pal.js:37:11)
      at Container.Object.<anonymous>.Container.invoke (node_modules/aurelia-dependency-injection/dist/commonjs/aurelia-dependency-injection.js:541:19)
      at ProviderResolver.get (node_modules/aurelia-templating/dist/commonjs/aurelia-templating.js:2305:72)
      at Container.Object.<anonymous>.Container.get (node_modules/aurelia-dependency-injection/dist/commonjs/aurelia-dependency-injection.js:493:28)
      at Container.elementContainerGet [as get] (node_modules/aurelia-templating/dist/commonjs/aurelia-templating.js:2360:15)
      at HtmlBehaviorResource.create (node_modules/aurelia-templating/dist/commonjs/aurelia-templating.js:4379:56)
      at applyInstructions (node_modules/aurelia-templating/dist/commonjs/aurelia-templating.js:2470:31)
      at ViewFactory.create (node_modules/aurelia-templating/dist/commonjs/aurelia-templating.js:2691:7)
      at TemplatingEngine.enhance (node_modules/aurelia-templating/dist/commonjs/aurelia-templating.js:5227:24)
      at node_modules/aurelia-framework/dist/commonjs/aurelia-framework.js:176:28

I have searched for a proper way to unittest this, but I'm unable to find a solution. Hopefully the community can help me out.

What is the expected behavior?
A possibility to run unittest that contains ValidationRules without it throwing an exception.

I have created a public repo where you can find all the files necessary: https://github.com/JordyThien/aurelia-unittest-validation-rules
Basically I created a new aurelia project using the aurelia CLI: au new aurelia-testing --unattended --select typescript,jest,vscode --here

I've updated the https://github.com/JordyThien/aurelia-unittest-validation-rules/blob/master/src/app.ts to contain ValidationRules
And I updated the spec to add aurelia-validation
Where running the tests using au test the exception will be thrown.