Reduce boilerplate in compiler JUnit tests (#5158)

Many JUnit tests share a compiler instance between all
test cases in a class to reduce overhead.

This commit refactors the mechanism to reduce the boilerplate.

In the new scheme:

  - Using the `@ClassRule` hook in JUnit, we create a per-class
    map for each test class.
  - Per-class values are registered from the test class itself
    by calling `cached("someKey", () => mkExpensiveThing)`
  - At the end of the test, the entries in this map are `close()`-ed
    (if they implement `Closable`), and are released for
    garbage collection.)

1 files changed, 1 insertions, 8 deletions

diff --git a/test/junit/scala/tools/nsc/backend/jvm/opt/MethodLevelOptsTest.scala b/test/junit/scala/tools/nsc/backend/jvm/opt/MethodLevelOptsTest.scala
index dd7fbd9977..003b2d4880 100644
--- a/test/junit/scala/tools/nsc/backend/jvm/opt/MethodLevelOptsTest.scala
+++ b/test/junit/scala/tools/nsc/backend/jvm/opt/MethodLevelOptsTest.scala
@@ -18,16 +18,9 @@ import ASMConverters._
 import scala.tools.testing.ClearAfterClass
 import scala.collection.JavaConverters._
 
-object MethodLevelOptsTest extends ClearAfterClass.Clearable {
-  var methodOptCompiler = newCompiler(extraArgs = "-Yopt:l:method")
-  def clear(): Unit = { methodOptCompiler = null }
-}
-
 @RunWith(classOf[JUnit4])
 class MethodLevelOptsTest extends ClearAfterClass {
-  ClearAfterClass.stateToClear = MethodLevelOptsTest
-
-  val methodOptCompiler = MethodLevelOptsTest.methodOptCompiler
+  val methodOptCompiler = cached("methodOptCompiler", () => newCompiler(extraArgs = "-Yopt:l:method"))
 
   def wrapInDefault(code: Instruction*) = List(Label(0), LineNumber(1, Label(0))) ::: code.toList ::: List(Label(1))