I'm facing problems related to string comparison using Assert.equals() provided by remix_tests.sol.

I made a toy contract and a related test to show what the problem is:


When I run that test on Remix IDE with Solidity v0.5.1+commit.c8a2cb62, the last Assert comparing a string and another one built from its bytes32 counterpart does not pass. I put both strings inside assert message to see what was compared and the output is:

1 failing

test_1 - Test user adding
Alice and Alice are not the same.

So, someone knows what is happening and how to make the string comparison work??

I tried to look for remix_tests.sol source code to study what was going on but I couldn't find it anywhere.

1 Answer 1


The issue with your code is the 000000000000000000000000000000000000000000000000000000 in 0x416c696365000000000000000000000000000000000000000000000000000000 are also decoded with the character \u0000.

To fix that, you can use this function bytes32ToString to decode correctly without the zeros:

import "remix_tests.sol"; // this import is automatically injected by Remix.
import "./ContainerContract.sol";

contract test_1 {

    ContainerContract container;

    function beforeAll () public {
       container = new ContainerContract();

    function testUserAdding() public returns (string memory) {
        // setup
        string memory name = "Alice";

        bytes32 nameBytes = 0x416c696365000000000000000000000000000000000000000000000000000000;

        // processing
        bytes32 recoveredNameBytes = container.data(0);
        string memory recoveredName = bytes32ToString(recoveredNameBytes);

        // asserting
        Assert.equal(nameBytes, recoveredNameBytes, "byte representations should be the same.");
        Assert.equal(name, name, "They should be literally the same.");
        string memory assertMsg = string(abi.encodePacked(name, " and ", recoveredName, " are not the same."));
        Assert.equal(name, recoveredName, assertMsg);

    function bytes32ToString(bytes32 x) public returns (string memory value) {
        bytes memory bytesString = new bytes(32);
        uint charCount = 0;
        for (uint j = 0; j < 32; j++) {
            byte char = byte(bytes32(uint(x) * 2 ** (8 * j)));
            if (char != 0) {
                bytesString[charCount] = char;
        bytes memory bytesStringTrimmed = new bytes(charCount);
        for (uint j = 0; j < charCount; j++) {
            bytesStringTrimmed[j] = bytesString[j];
        value = string(bytesStringTrimmed);
  • Just for clarification, byte(bytes32(uint(x) * 2 ** (8 * j))) takes the jth byte starting from the left, right? so with x=nameBytes and j=0 it would pick 41, correct?? Jul 22, 2019 at 14:07

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