By default Mocha will read a file named test/mocha.opts that can contain command line arguments. So you could create such a file that contains:
--timeout 5000
Whenever you run Mocha at the command line, it will read this file and set a timeout of 5 seconds by default.
Another way which may be better depending on your situation is to set it like this in a top level describe call in your test file:
describe("something", function () {
this.timeout(5000);
// tests...
});
This would allow you to set a timeout only on a per-file basis.
You could use both methods if you want a global default of 5000 but set something different for some files.
Note that you cannot generally use an arrow function if you are going to call this.timeout (or access any other member of this that Mocha sets for you). For instance, this will usually not work:
describe("something", () => {
this.timeout(5000); //will not work
// tests...
});
This is because an arrow function takes this from the scope the function appears in. Mocha will call the function with a good value for this but that value is not passed inside the arrow function. The documentation for Mocha says on this topic:
Passing arrow functions (“lambdas”) to Mocha is discouraged. Due to the lexical binding of this, such functions are unable to access the Mocha context.