do you write test code before your javascript code code example

Example: write test code javascript

// create directory

// npm init -y
// npm install tape

// create a file example: filename.js
// create a function in it and export as module.exports = functionName
// create a test file example: filename.test.js
// import the exported function as const functionName = require(./name)

test('textContent' t =>{
     const actual = //something;
     const expected = // something;
     
     t.equal = (actual, expected);
	 t.end();
     });