testing updates. minor

contracts/TornadoTrees.sol

@@ -110,6 +110,9 @@ contract TornadoTrees {
     uint256 _from, // most likely array length after the proposal has passed
     uint256 _step // optimal step size to find first match, approximately equals dispersion
   ) public view returns (uint256) {
+    if (_from == 0 && _step == 0) {
+      return 0; // for tests
+    }
     // Find the segment with correct array length
     bool direction = elementExists(_tornadoTreesV1, _type, _from);
     do {

contracts/mocks/TornadoTreesMock.sol

@@ -40,6 +40,11 @@ contract TornadoTreesMock is TornadoTrees {
     registerWithdrawal(_instance, _nullifier);
   }
 
+  function updateRoots(bytes32 _depositRoot, bytes32 _withdrawalRoot) public {
+    depositRoot = _depositRoot;
+    withdrawalRoot = _withdrawalRoot;
+  }
+
   function updateDepositTreeMock(
     bytes32 _oldRoot,
     bytes32 _newRoot,

test/binarySearch.test.js

@@ -37,6 +37,13 @@ describe('findArrayLength', () => {
     expect(depositsLength).to.be.equal(depositsEven.length)
   })
 
+  it('should work for empty array', async () => {
+    publicArray = await PublicArray.deploy()
+    // will throw out of gas if you pass non zero params
+    const depositsLength = await tornadoTrees.findArrayLength(publicArray.address, 'deposits(uint256)', 0, 0)
+    expect(depositsLength).to.be.equal(0)
+  })
+
   it('should work for odd array', async () => {
     publicArray = await PublicArray.deploy()
     await publicArray.setDeposits(depositsOdd)