Assign name to root project while keeping the default aggregation - sbt

Question

I have a fairly large sbt project (about 30 sub-projects). From what I've figured out, sbt will use the name of the root directory as the name of the root project, if none is declared explicitly in build.sbt. Depending on where the project is checked out, e.g. in a CI environment, that name may change. I'm currently using sbt 1.2.8.
My issue is that I would like to assign a stable name to the root project so that I can e.g. run all tests using sbt root/test [0], leveraging the default aggregation of the root project over all sub-projects. The only way I have found so far to assign a name to the root project is by explicitly declaring the project. But this will disable the default aggregation.
Is there a way to assign a name to the root project that will keep the default aggregation over all sub-projects? Or is there another way to access the root project on the command line without relying on it's name?
[0]: The default project is changed by the build.sbt using onLoad in Global := (Command.process("project ...", _)) compose (onLoad in Global).value. So just running sbt test won't work.

Answer 1

Here is a potential solution without having to explicitly refer to the root project.
Given the following project structure consisting of root project, and sub-projects core and util
build.sbt
core
project
src
target
util
and the following build definition in build.sbt
lazy val util = (project in file("util"))
lazy val core = (project in file("core"))
onLoad in Global := { Command.process("project util", _: State) } compose (onLoad in Global).value
ThisBuild / libraryDependencies += "org.scalatest" %% "scalatest" % "3.0.5" % Test
we could run tests from all projects whilst being in any particular sub-project by defining a custom task testAll which evaluates test using inAnyProject scope filter
val testAll = taskKey[Unit]("Run tests in all projects whilst being in any particular sub-project")
ThisBuild / testAll := Def.taskDyn {
(Test / test).all(ScopeFilter(inAnyProject))
}.value
Now executing sbt will load util sub-project by default, nevertheless testAll should run all tests from all projects:
sbt:util> testAll
[info] RootSpec:
[info] The Root object
[info] - should say root hello
[info] UtilSpec:
[info] The Util object
[info] - should say util hello
[info] CoreSpec:
[info] The Core object
[info] - should say core hello
[info] Run completed in 349 milliseconds.
[info] Total number of tests run: 1
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 1, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.
[info] Run completed in 309 milliseconds.
[info] Total number of tests run: 1
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 1, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.
[info] Run completed in 403 milliseconds.
[info] Total number of tests run: 1
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 1, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.
[success] Total time: 1 s, completed 11-Apr-2019 16:29:26
sbt:util>
where RootSpec, CoreSpec, and UtilsSpec are at
src/test/scala/example/RootSpec.scala
core/src/test/scala/example/CoreSpec.scala
util/src/test/scala/example/UtilSpec.scala