Fixed reference test

public/biopet-core/src/test/scala/nl/lumc/sasc/biopet/core/ReferenceTest.scala

@@ -19,6 +19,7 @@ class ReferenceTest extends TestNGSuite with Matchers with MockitoSugar {
 
   @Test
   def testDefault: Unit = {
+    Logging.errors.clear()
     make(config :: testReferenceNoIndex :: Nil).referenceFasta()
     Logging.checkErrors(true)
 

public/biopet-utils/src/main/scala/nl/lumc/sasc/biopet/utils/Logging.scala

@@ -36,7 +36,7 @@ trait Logging {
 object Logging {
   val logger = Logger.getRootLogger
 
-  private val errors: ListBuffer[Exception] = ListBuffer()
+  private[biopet] val errors: ListBuffer[Exception] = ListBuffer()
 
   def addError(error: String, debug: String = null): Unit = {
     val msg = error + (if (debug != null && logger.isDebugEnabled) "; " + debug else "")