The actual amount of the token owner not shown as expected - ethereum

Question

I created an ERC20 SC, this is the initial supply amount 100000000000. But, when I run unit test (truffle test) to show the total balance amount of the accounts[0] and the actual amount is 99999998877, expected amount should be 100000000000. Can someone explain to me, why that's happened?
Thank you.
it("should return the total supply", function() {
return CToken.deployed().then(function(instance){
return tokenInstance.totalSupply.call();
}).then(function(result){
assert.equal(result.toNumber(), 100000000000, 'total supply is wrong');
})
});
it("should return the balance of token owner", function() {
var token;
return CToken.deployed().then(function(instance){
token = instance
return tokenInstance.balanceOf.call(accounts[0]);
}).then(function(result){
assert.equal(result.toNumber(), 99999998877, 'balance is wrong');
})
});
Contract code:
pragma solidity >=0.4.21 <0.6.0;
import "../node_modules/openzeppelin-solidity/contracts/token/ERC20/StandardToken.sol";
import "../node_modules/openzeppelin-solidity/contracts/ownership/Ownable.sol";
/**
* #title BearToken is a basic ERC20 Token
*/
contract CToken is StandardToken, Ownable{
uint256 public totalSupply;
string public name;
string public symbol;
uint32 public decimals;
/**
* #dev assign totalSupply to account creating this contract
*/
constructor() public {
symbol = "CT";
name = "CToken";
decimals = 18;
totalSupply = 100000000000;
owner = msg.sender;
balances[msg.sender] = totalSupply;
//emit Transfer(0x0, msg.sender, totalSupply);
}
}

Answer 1

Your total supply is 10^29 (10^11 tokens, each token has 10^18 decimal points), which is not something javascript number can safely handle. https://docs.ethers.io/ethers.js/html/notes.html#why-can-t-i-just-use-numbers
web3 returns a BN instance, don't convert it to number.
You can assert like this:
const BN = web3.utils.BN
const ten = new BN("10")
const expected = ten.pow(new BN("27"))
assert(result.eq(expected), "Result doesn't match expected value")