Run JUnit tests with SBT - unit-testing

Question

I have a 0.13.7 SBT project, with several sub-projects.
One of them is called webapp, and it has many JUnit tests in webapp/src/test/java.
When running:
sbt webapp/test
only the ScalaTest tests are run, but no JUnit tests.
Snippet of my build.sbt file:
libraryDependencies ++= Seq(
"com.novocode" % "junit-interface" % "0.11" % Test
)
lazy val webapp = project
settings(
Seq(
projectDependencies ++= Seq(
....
"org.scalatest" %% "scalatest" % "2.2.2" % Test,
"junit" % "junit" % "4.11" % Test,
"com.novocode" % "junit-interface" % "0.11" % Test
)
): _*
)
Example JUnit test:
import org.junit.Test;
public class CodificadorBase64Test {
#Test
public void testPlain() {
byte b[] = {64, 127, 72, 36, 100, 1, 5, 9, 123};
assertEquals("QH9IJGQBBQl7", CodificadorBase64.encode(b));
}
}
UPDATE (some more research):
> webapp/testFrameworks
[info] List(TestFramework(WrappedArray(org.scalacheck.ScalaCheckFramework)), TestFramework(WrappedArray(org.specs2.runner.Specs2Framework, org.specs2.runner.SpecsFramework)), TestFramework(WrappedArray(org.specs.runner.SpecsFramework)), TestFramework(WrappedArray(org.scalatest.tools.Framework, org.scalatest.tools.ScalaTestFramework)), TestFramework(WrappedArray(com.novocode.junit.JUnitFramework))
show webapp/loadedTestFrameworks
[info] Map(TestFramework(WrappedArray(
org.scalatest.tools.Framework,
org.scalatest.tools.ScalaTestFramework)
) -> org.scalatest.tools.Framework#65767aeb)
So JUnit support is known by SBT but not loaded.
Debug output:
[debug] Framework implementation 'org.scalacheck.ScalaCheckFramework' not present.
[debug] Framework implementation 'org.scalacheck.ScalaCheckFramework' not present.
[debug] Framework implementation 'org.scalacheck.ScalaCheckFramework' not present.
[debug] Framework implementation 'org.scalacheck.ScalaCheckFramework' not present.
[debug] Framework implementation 'org.specs2.runner.Specs2Framework' not present.
[debug] Framework implementation 'org.specs2.runner.Specs2Framework' not present.
[debug] Framework implementation 'org.specs2.runner.Specs2Framework' not present.
[debug] Framework implementation 'org.specs2.runner.Specs2Framework' not present.
[debug] Framework implementation 'org.specs2.runner.SpecsFramework' not present.
[debug] Framework implementation 'org.specs2.runner.SpecsFramework' not present.
[debug] Framework implementation 'org.specs2.runner.SpecsFramework' not present.
[debug] Framework implementation 'org.specs2.runner.SpecsFramework' not present.
[debug] Framework implementation 'org.specs.runner.SpecsFramework' not present.
[debug] Framework implementation 'org.specs.runner.SpecsFramework' not present.
[debug] Framework implementation 'org.specs.runner.SpecsFramework' not present.
[debug] Framework implementation 'org.specs.runner.SpecsFramework' not present.
[debug] Framework implementation 'com.novocode.junit.JUnitFramework' not present.
[debug] Framework implementation 'com.novocode.junit.JUnitFramework' not present.
[debug] Framework implementation 'com.novocode.junit.JUnitFramework' not present.
[debug] Framework implementation 'com.novocode.junit.JUnitFramework' not present.
[debug] Subclass fingerprints: List((org.scalatest.Suite,false,org.scalatest.tools.Framework$$anon$1#3ad42aff))
[debug] Subclass fingerprints: List((org.scalatest.Suite,false,org.scalatest.tools.Framework$$anon$1#97f54b))
[debug] Annotation fingerprints: List((org.scalatest.WrapWith,false,org.scalatest.tools.Framework$$anon$2#6a589982))
[debug] Annotation fingerprints: List((org.scalatest.WrapWith,false,org.scalatest.tools.Framework$$anon$2#1b95d5e6))
[debug] Subclass fingerprints: List((org.scalatest.Suite,false,org.scalatest.tools.Framework$$anon$1#5c997dac))
[debug] Subclass fingerprints: List((org.scalatest.Suite,false,org.scalatest.tools.Framework$$anon$1#406c43ef))
[debug] Annotation fingerprints: List((org.scalatest.WrapWith,false,org.scalatest.tools.Framework$$anon$2#282ddefc))
[debug] Annotation fingerprints: List((org.scalatest.WrapWith,false,org.scalatest.tools.Framework$$anon$2#4400c80))
Working with:
SBT 0.13.9, and
JUnit 4.x.
Related information:
Why don't junit tests get executed with "sbt test"?
SBT documentation

Answer 1

Finally, I've discovered, that I have to add the following settings to the subproject:
lazy val webapp = project
settings(
Seq(
projectDependencies ++= Seq(
....
"org.scalatest" %% "scalatest" % "2.2.2" % Test,
"junit" % "junit" % "4.11" % Test,
crossPaths := false,
"com.novocode" % "junit-interface" % "0.11" % Test
)
): _*
)
It is important to declare the junit-interface dependency in the subproject, and in addition, to set to false the crossPaths setting.
The clue has been given by this issue.
If the main project doesn't have JUnit tests, then the needed test settings, don't need to be provided.
In addition, for knowing the failing method and the cause, we need this setting:
testOptions in Test := Seq(Tests.Argument(TestFrameworks.JUnit, "-a"))

Answer 2

This question about supporting JUnit in SBT has been asked multiple times with slightly different framings.
Multiple hits made it hard for me to find the simplest and most current answer.
This answer by #david.perez seems clear and works with current (2018) SBT 1.1.4.
(That particular question was about conflicting JUnit versions. The exclude("junit", "junit-dep") may not be necessary.)
I'll also copy-paste the code here for quick access:
libraryDependencies ++= Seq(
"junit" % "junit" % "4.12" % Test,
"com.novocode" % "junit-interface" % "0.11" % Test exclude("junit", "junit-dep")
)