There doesn't seem to be a test for the color argument.

My solution was able to pass even though it always set the cells to '⬛'

Tests break on Node 12.x and above:

TypeError: Math.random is not a function
    at nanoid (/workspace/node/node_modules/.pnpm/nanoid@3.1.20/node_modules/nanoid/non-secure/index.cjs:25:29)
    at Object.exports.uniqueID (/workspace/node/node_modules/.pnpm/mocha@8.3.0/node_modules/mocha/lib/utils.js:717:26)
    at Object.exports.assignNewMochaID (/workspace/node/node_modules/.pnpm/mocha@8.3.0/node_modules/mocha/lib/utils.js:720:22)
    at Test.Runnable (/workspace/node/node_modules/.pnpm/mocha@8.3.0/node_modules/mocha/lib/runnable.js:43:9)
    at new Test (/workspace/node/node_modules/.pnpm/mocha@8.3.0/node_modules/mocha/lib/test.js:32:12)
    at context.it.context.specify (/workspace/node/node_modules/.pnpm/mocha@8.3.0/node_modules/mocha/lib/interfaces/bdd.js:87:18)
    at Suite.<anonymous> (/workspace/node/test.js:100:3)
    at Object.create (/workspace/node/node_modules/.pnpm/mocha@8.3.0/node_modules/mocha/lib/interfaces/common.js:148:19)
    at context.describe.context.context (/workspace/node/node_modules/.pnpm/mocha@8.3.0/node_modules/mocha/lib/interfaces/bdd.js:42:27)
    at /workspace/node/test.js:95:1
    at Object.<anonymous> (/workspace/node/test.js:175:3)
    at Module._compile (internal/modules/cjs/loader.js:999:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1027:10)
    at Module.load (internal/modules/cjs/loader.js:863:32)
    at Function.Module._load (internal/modules/cjs/loader.js:708:14)
    at Module.require (internal/modules/cjs/loader.js:887:19)
    at require (internal/modules/cjs/helpers.js:74:18)
    at Object.exports.requireOrImport (/workspace/node/node_modules/.pnpm/mocha@8.3.0/node_modules/mocha/lib/esm-utils.js:42:12)
    at Object.exports.loadFilesAsync (/workspace/node/node_modules/.pnpm/mocha@8.3.0/node_modules/mocha/lib/esm-utils.js:55:34)
    at Mocha.loadFilesAsync (/workspace/node/node_modules/.pnpm/mocha@8.3.0/node_modules/mocha/lib/mocha.js:431:19)
    at singleRun (/workspace/node/node_modules/.pnpm/mocha@8.3.0/node_modules/mocha/lib/cli/run-helpers.js:125:15)
    at exports.runMocha (/workspace/node/node_modules/.pnpm/mocha@8.3.0/node_modules/mocha/lib/cli/run-helpers.js:190:10)
    at Object.exports.handler (/workspace/node/node_modules/.pnpm/mocha@8.3.0/node_modules/mocha/lib/cli/run.js:362:11)
    at /workspace/node/node_modules/.pnpm/yargs@16.2.0/node_modules/yargs/build/index.cjs:443:71

• your logs are misleading, for now, even if the intent is good: which one is eactual and which one is expected?
• looking at the logs of the 25x25, at 10,13 for the center... looks like what you said about the axis is totally wrong, isn't? => x is horizontal going right, and y is vertical going... down!? See, talking about "is rows... us columns" doesn't tell if you're talking about the indexes of the axis...

consider this one as a very strong suggestion:

in the sample tests, you should show the strings using multiline ones. This way the expecte'd result is immediatly visible from the user.

x are columns

• you need to precise that x is going down, just like usual in a 2D array.
• the description and the tests are expecially confusing about wht should be returned: string? array?
  • string is visible in the sample tests, but you use an unknown custom assertion function
  • the description doesn't say anythig really clear about that
  • the assertions are showing that 2D arrays are tested... => what the user is supposed to return, actually?
    => you have to be pretty clear about that

Duplicate

The task is not explained at all.