Fix clear operation in ListBuffer

collections/src/main/scala/strawman/collection/mutable/ListBuffer.scala

@@ -94,6 +94,9 @@ class ListBuffer[A]
 
   def clear(): Unit = {
     first = Nil
+    len = 0
+    last0 = null
+    aliased = false
   }
 
   def addOne(elem: A): this.type = {

test/junit/src/test/scala/strawman/collection/mutable/ListBufferTest.scala

@@ -0,0 +1,30 @@
+package strawman.collection.mutable
+
+import strawman.collection.immutable.Nil
+
+import org.junit.{Assert, Test}
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+
+@RunWith(classOf[JUnit4])
+class ListBufferTest {
+
+  @Test
+  def hasCorrectClear(): Unit = {
+    val b = ListBuffer.empty[String]
+    b += "a"
+    Assert.assertTrue(b.sameElements("a" :: Nil))
+    b.clear()
+    Assert.assertEquals(ListBuffer.empty[String], b)
+    b += "b"
+    Assert.assertTrue(b.sameElements("b" :: Nil))
+
+    val b2 = ListBuffer.empty[String]
+    b2 += "a"
+    val _ = b2.toList
+    b2.clear()
+    b2 += "b"
+    Assert.assertTrue(b2.sameElements("b" :: Nil))
+  }
+
+}