SBT how to add unmanaged jars to subproject tests? - scala

Question

I have an SBT multiproject structure, but for some reason sbt does not recognize the unmanaged jar when tests are run. The objective is to have a stub subproject without an actual implementation and add this as a "Provided" dependency to the Main class, it should detect the jars in the /lib folder when provided. The actual implementation in the .jar file simply prints a random string.
Here is the project structure.
./MainClass
./MainClass/lib/printsomethingexample_2.13-0.1.0-SNAPSHOT.jar
./MainClass/src/test/scala/Main.scala
./MainClass/src/main/scala/Main.scala
./stub/lib/printsomethingexample_2.13-0.1.0-SNAPSHOT.jar
./stub/src/main/scala/test/stub/Example.scala
./build.sbt
File main/scala/Main.scala
import test.stub.Example
object Main extends App {
Example.printSomething()
}
File test/scala/Main.scala
import org.scalatest.flatspec._
import test.stub.Example
class Main extends AnyFlatSpec {
"Unmanaged jar" should "work" in {
Example.printSomething()
}
}
scala/test/stub/Example.scala:
package test.stub
object Example {
def printSomething(): Unit = ???
}
build.sbt:
ThisBuild / version := "0.1.0-SNAPSHOT"
ThisBuild / scalaVersion := "2.13.10"
lazy val root = (project in file("."))
.settings(
name := "stubExample"
).aggregate(MainClass, stub)
lazy val stub = project
.in(file("stub"))
.settings(
name := "stub"
)
lazy val MainClass = project
.in(file("MainClass"))
.settings(
name := "MainClass",
libraryDependencies += "org.scalatest" %% "scalatest" % "3.2.14" % Test,
).dependsOn(`stub` % Provided)
When I run sbt "MainClass/runMain Main" it finds the unmanaged jars as expected and prints the string, but when I run sbt "MainClass/test" I get the following error:
[info] Main:
[info] Unmanaged jar
[info] - should work *** FAILED ***
[info] scala.NotImplementedError: an implementation is missing
Does anyone understand why the jars are not found?
*** EDIT ***
Here is the output of sbt "MainClass/runMain Main"
▶ sbt "MainClass/runMain Main"
[info] welcome to sbt 1.6.2 (Azul Systems, Inc. Java 1.8.0_312)
[info] loading global plugins from /Users/riccardo/.sbt/1.0/plugins
[info] loading project definition from /Users/riccardo/Documents/Projects/stubExample/project
[info] loading settings for project root from build.sbt ...
[info] set current project to stubExample (in build file:/Users/riccardo/Documents/Projects/stubExample/)
[info] running Main
Printed Something
The .jar has an implementation of test.stub.Example#printSomething (It is a different project)
package test.stub
object Example {
def printSomething(): Unit = println("Printed Something")
}
My expectation is that since the stub subproject is marked as Provided it should use the printSomething implementation from the jar in the classpath instead of the stub subproject, the stub subproject was marked as Provided and would expect it to be excluded from the classpath (maybe I don't understand how Provided works).
This behavior happens when running the main class as shown above, it uses the printSomething from the classpath in lib/printsomethingexample_2.13-0.1.0-SNAPSHOT.jar instead of using the stub that is not implemented. In my real life scenario, I need the dependency on the stub subproject.
If I remove the dependsOn the sbt test step works, but the project wouldn't compile without the unmanaged jars in the /lib folder, hence why we use a stub subproject as dependecy, just to make the project compile.