Added unit tests

Author: leerho

src/main/java/com/yahoo/sketches/theta/Sketch.java

@@ -231,7 +231,8 @@ public double getLowerBound(final int numStdDev) {
 
   /**
    * Returns the maximum number of storage bytes required for a CompactSketch with the given
-   * number of actual entries.
+   * number of actual entries. Note that this assumes the worse case of the sketch in
+   * estimation mode, which requires storing theta and count.
    * @param numberOfEntries the actual number of entries stored with the CompactSketch.
    * @return the maximum number of storage bytes required for a CompactSketch with the given number
    * of entries.

src/test/java/com/yahoo/sketches/theta/ConcurrentDirectQuickSelectSketchTest.java

@@ -686,6 +686,15 @@ public void checkConstructReconstructFromMemory() {
     }
   }
 
+  @Test
+  public void checkNullMemory() {
+    UpdateSketchBuilder bldr = new UpdateSketchBuilder();
+    final UpdateSketch sk = bldr.build();
+    for (int i = 0; i < 1000; i++) { sk.update(i); }
+    final UpdateSketch shared = bldr.buildSharedFromSketch(sk, null);
+    assertEquals(shared.getRetainedEntries(), 1000);
+    assertFalse(shared.hasMemory());
+  }
 
   //checks Alex's bug where lgArrLongs > lgNomLongs +1.
   @Test