Add AddBatch CaseB

CASE B: ALMOST CASE A, Almost empty Tree --> if Tree has numLeafs < minLeafsThreshold
==============================================================================
- Get the Leafs (key & value) (iterate the tree from the current root getting
the leafs)
- Create a new empty Tree
- Do CASE A for the new Tree, giving the already existing key&values (leafs)
from the original Tree + the new key&values to be added from the AddBatch call

       R                 R
      / \               /  \
     A   *             /    \
        / \           /      \
       B   C         *        *
                    / |      / \
                   /  |     /   \
                  /   |    /     \
           L:    A    B   G       D
                         / \
                        /   \
                       /     \
                      C      *
                            / \
                           /   \
                          /     \
                         ...     ... (nLeafs < minLeafsThreshold)

addbatch_test.go

@@ -49,3 +49,53 @@ func TestAddBatchCaseA(t *testing.T) {
 	// check that both trees roots are equal
 	c.Check(tree2.Root(), qt.DeepEquals, tree.Root())
 }
+
+func TestAddBatchCaseB(t *testing.T) {
+	c := qt.New(t)
+
+	nLeafs := 1024
+
+	tree, err := NewTree(memory.NewMemoryStorage(), 100, HashFunctionPoseidon)
+	c.Assert(err, qt.IsNil)
+	defer tree.db.Close()
+
+	start := time.Now()
+	for i := 0; i < nLeafs; i++ {
+		k := BigIntToBytes(big.NewInt(int64(i)))
+		v := BigIntToBytes(big.NewInt(int64(i * 2)))
+		if err := tree.Add(k, v); err != nil {
+			t.Fatal(err)
+		}
+	}
+	fmt.Println(time.Since(start))
+
+	tree2, err := NewTree(memory.NewMemoryStorage(), 100, HashFunctionPoseidon)
+	c.Assert(err, qt.IsNil)
+	defer tree2.db.Close()
+
+	// add the initial leafs to fill a bit the tree before calling the
+	// AddBatch method
+	for i := 0; i < 99; i++ { // TMP TODO use const minLeafsThreshold-1 once ready
+		k := BigIntToBytes(big.NewInt(int64(i)))
+		v := BigIntToBytes(big.NewInt(int64(i * 2)))
+		if err := tree2.Add(k, v); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	var keys, values [][]byte
+	for i := 99; i < nLeafs; i++ {
+		k := BigIntToBytes(big.NewInt(int64(i)))
+		v := BigIntToBytes(big.NewInt(int64(i * 2)))
+		keys = append(keys, k)
+		values = append(values, v)
+	}
+	start = time.Now()
+	indexes, err := tree2.AddBatchOpt(keys, values)
+	c.Assert(err, qt.IsNil)
+	fmt.Println(time.Since(start))
+	c.Check(len(indexes), qt.Equals, 0)
+
+	// check that both trees roots are equal
+	c.Check(tree2.Root(), qt.DeepEquals, tree.Root())
+}