If I have an SBT multi-project build, how can I make A's test dependencies not leak in to B's tests

Question

So, I have an SBT project with modules A and B.

• A depends on B.
• A and B's normal project packages are compatible.
• A has a package for testing that is incompatible with a package that B uses for tests.
• A does not depend on B's test packages
• A's tests fail, because of the test package incompatibility

In my eyes, this failure is invalid, because A's tests do not depend on B's tests.

I'm using

A.dependsOn(B % "compile->compile;test->compile")

meaning

• A's compile depends on B's compile
• A's test depends on B's compile.

Am I doing something wrong?

Here's the actual build file . Relevant project is doobieSupport23 depending on core

Here's the build error . You can see that it's pulling in scalaz 7.2 in the build, but it should only be pulling scalaz 7.1.6

Answer 1

The problem is definitely not in projects depending on each other, the configuration "compile->compile;test->compile" , as it seems to me, is perfectly valid for what you need to achieve.

What's causing the problem is that your libraryDependencies are shared due to A being dependent on B. Fortunately, sbt allows to manage dependencies quite precisely.

The easiest suggestion would be to apply a newer version of the conflicting dependency to a scope as narrow as possible - meaning, if scalaz 7.2.0 is only needed in core's tests, so be it!

lazy val core = project(...)
  .settings(libraryDependencies in Test += "org.scalaz" %% "scalaz" % "7.2.0")
lazy val doobieSupport23 = project(...).dependsOn(core)
  .settings(libraryDependencies in Test += "org.scalaz" %% "scalaz" % "7.1.6")

If you can't make it work because the newer version is actually used in other core's dependencies, the following trick may do it:

val scalazOld = "org.scalaz" %% "scalaz" % "7.1.6"
val scalazNew = "org.scalaz" %% "scalaz" % "7.2.0"

lazy val core = project(...)
  .settings(libraryDependencies += "org.scalaz" %% "scalaz" % "7.2.0")

lazy val doobieSupport23 = project(...).dependsOn(core)
  .settings(
    libraryDependencies in Test += "org.scalaz" %% "scalaz" % "7.1.6" force()
  )

Note the force() combinator. I'm not sure this way it won't fail in runtime due to incompatible classes in classpath.

Answer 2

What I had specified in the issue works exactly as expected.

The problem ended up being that my build file had an extraneous dependency that I had just glossed over. That dependency was causing doobie 3.0 being pulled in where I only expected doobie 2.3.