j2k: flatten test cases and testData directory structure

Move j2k/test/tests -> j2k/tests, j2k/test/testData -> j2k/testData

j2k/testData/fileOrElement/mutableCollections/Recursion.java

@@ -0,0 +1,16 @@
+import java.util.*;
+
+class A {
+    void foo(Collection<String> collection) {
+        bar(collection);
+    }
+
+    void bar(Collection<String> collection) {
+        if (collection.size() < 5) {
+            foo(collection);
+        }
+        else {
+            collection.add("a")
+        }
+    }
+}