Fix ScalaLibrary again

I was benchmarking sbt with turbo mode on and found that tests weren't
running. This was because we were inadvertently excluding all of the
dependency jars from the dynamic classpath. I have no idea why the
scripted tests didn't catch this.

The scalatest scripted test didn't catch this because 'test' just
automaticaly succeeds if no test frameworks are found. To guard against
regression, I had to ensure that 'test' failed for every strategy if a
bad test file was present.

main/src/main/scala/sbt/internal/ClassLoaders.scala

@@ -132,7 +132,6 @@ private[sbt] object ClassLoaders {
           case _: AllLibraryJars => true
           case _                 => false
         }
-        val allDependenciesSet = allDependencies.toSet
         val scalaLibraryLayer = layer(si.libraryJars, interfaceLoader, cache, resources, tmp)
         val cpFiles = fullCP.map(_._1)
 
@@ -148,7 +147,10 @@ private[sbt] object ClassLoaders {
           else resourceLayer
 
         // layer 4
-        val dynamicClasspath = cpFiles.filterNot(allDependenciesSet ++ si.libraryJars)
+        val filteredSet =
+          if (layerDependencies) allDependencies.toSet ++ si.libraryJars
+          else Set(si.libraryJars: _*)
+        val dynamicClasspath = cpFiles.filterNot(filteredSet)
         new LayeredClassLoader(dynamicClasspath, dependencyLayer, resources, tmp)
     }
     ClasspathUtilities.filterByClasspath(cpFiles, raw)

sbt/src/sbt-test/classloader-cache/package-private/test

@@ -1,3 +1,5 @@
+> set Compile / classLoaderLayeringStrategy := ClassLoaderLayeringStrategy.AllLibraryJars
+
 -> run
 
 > set Compile / classLoaderLayeringStrategy := ClassLoaderLayeringStrategy.Flat

sbt/src/sbt-test/classloader-cache/scalatest/test

@@ -1,3 +1,5 @@
+> set Test / classLoaderLayeringStrategy := ClassLoaderLayeringStrategy.AllLibraryJars
+
 > test
 
 > set Test / classLoaderLayeringStrategy := ClassLoaderLayeringStrategy.Flat
@@ -8,8 +10,14 @@
 
 > test
 
-> set Test / classLoaderLayeringStrategy := ClassLoaderLayeringStrategy.AllLibraryJars
-
 $ copy-file changes/bad.scala src/test/scala/sbt/ScalatestTest.scala
 
 -> test
+
+> set Test / classLoaderLayeringStrategy := ClassLoaderLayeringStrategy.Flat
+
+-> test
+
+> set Test / classLoaderLayeringStrategy := ClassLoaderLayeringStrategy.AllLibraryJars
+
+-> test