VSCode test runner shows failure correctly, but mill test reports success

[Code-Pudding]

I’m seeing different behavior between running ZIO tests inside VSCode and running them through Mill on the command line.

Build definition

extends: [ScalaModule, TestModule.ZioTest]
scalaVersion: 3.8.1
testFramework: zio.test.sbt.ZTestFramework
mvnDeps:
  - dev.zio::zio:2.1.26
  - dev.zio::zio-test:2.1.26

Test code

package foo

import zio.test.*

object FooTestsSpec extends ZIOSpecDefault {
  def spec =
    suite("FooTestsSpec")(
      test("simple") {
        assertTrue(false) // should intentionally fail
      }
    )
}

What I observe

• When I run the test using the little “Run Test” button in VSCode, the test runs and correctly reports a failure.
• When I run the same test using mill test, Mill reports success, even though the test should fail.

No further output, just a SUCCESS message:

mill test
131] test.compile compiling 1 Scala source to out/test/compile.dest/classes ...
131] done compiling
138-0] 
138/138, SUCCESS] mill test 2s

Question

Why does the VSCode test runner correctly detect the failure, but mill test reports success?
Is there something missing in my Mill configuration for ZIO Test, or is there a known issue with TestModule.ZioTest and ZTestFramework?