Fixes checkInvariants() not calling child nodes.

Author: brianburton

src/main/java/org/javimmutable/collections/array/FullBranchTrieNode.java

@@ -164,6 +164,9 @@ public void checkInvariants()
         if (entries.length != 32) {
             throw new IllegalStateException("unexpected entries size: expected=32 actual=" + entries.length);
         }
+        for (TrieNode<T> entry : entries) {
+            entry.checkInvariants();
+        }
     }
 
     private TrieNode<T> createUpdatedEntries(int shift,

src/main/java/org/javimmutable/collections/array/LeafTrieNode.java

@@ -131,7 +131,6 @@ public TrieNode<T> delete(int shift,
             sizeDelta.subtract(1);
             return of();
         } else {
-            assert shift > 0;
             return this;
         }
     }

src/main/java/org/javimmutable/collections/array/MultiBranchTrieNode.java

@@ -253,6 +253,9 @@ public void checkInvariants()
         if (entries.length != Integer.bitCount(bitmask)) {
             throw new IllegalStateException("unexpected entries size: expected=" + Integer.bitCount(bitmask) + " actual=" + entries.length);
         }
+        for (TrieNode<T> entry : entries) {
+            entry.checkInvariants();
+        }
     }
 
     // for use by unit tests

src/main/java/org/javimmutable/collections/array/SingleBranchTrieNode.java

@@ -175,6 +175,7 @@ public void checkInvariants()
         if (branchIndex < 0 || branchIndex >= 32) {
             throw new IllegalStateException("illegal branchIndex value: " + branchIndex);
         }
+        child.checkInvariants();
     }
 
     // for tests

src/test/java/org/javimmutable/collections/array/JImmutableTrieArrayTest.java

@@ -88,8 +88,21 @@ public void testRandom()
         for (int loop = 1; loop <= 20000; ++loop) {
             int index = r.nextInt(2000) - 1000;
             int value = r.nextInt();
-            array = array.assign(index, value);
-            expected.put(index, value);
+            switch (r.nextInt(4)) {
+                case 0:
+                case 1:
+                    array = array.assign(index, value);
+                    expected.put(index, value);
+                    break;
+                case 2:
+                    array = array.delete(index);
+                    expected.remove(index);
+                    break;
+                case 3:
+                    assertEquals(array.find(index).getValueOrNull(), array.get(index));
+                    array.checkInvariants();
+                    break;
+            }
         }
         assertEquals(expected.size(), array.size());
         for (Map.Entry<Integer, Integer> entry : expected.entrySet()) {