Couldn't find 'dub_test_root'. Make sure you are running tests with dub test

Hey, I'm trying to check this out, and I get this right now. Not sure why:

> Executing task: dub test <

Non-selected package unit-threaded is available with version 0.7.49.
Use "dub upgrade" to perform those changes.
Executable configuration "unittest" of package optional defines no main source file, this may cause certain build modes to fail. Add an explicit "mainSourceFile" to the package description to fix this.
Running custom 'unittest' configuration.
Performing "unittest" build using dmd for x86_64.
bolts 0.7.1: target for configuration "library" is up to date.
optional 0.4.1+commit.59.gff28b9f: building configuration "unittest"...
../../.dub/packages/silly-0.0.2/silly/silly.d(6,2): Error: static assert:  "Couldn't find 'dub_test_root'. Make sure you are running tests with dub test"
dmd failed with exit code 1.

I do have a custom unittest configuration because I have a separate tests folder as well as inline unittests. So I had this:

configurations": [
        {
            "name": "unittest",
            "importPaths": [
                "./tests"
            ],
            "sourcePaths": [
                "./tests"
            ],
            "targetType": "executable",
            "dependencies": {
                "silly": "~>0.0.2"
            }
        },

And just to check, I tried putting my entire "tests" folder under my source folder to match dub requirements, then it build but there's a

dmd failed with exit code -11.
The terminal process terminated with exit code: 2

Only if I have silly as a dep though.

Cheers!