alphanumeric generator generating empty strings

💬 Question and Help

I’m working on testing a validator that accepts a string starting with a letter followed by alphanumeric characters with fast-check. I have this code:

 it('should return on true on valid generated inputs', () => {
    const alphanumericChar = fc.mapToConstant(
      { num: 26, build: (v) => String.fromCharCode(v + 0x61) },
      { num: 10, build: (v) => String.fromCharCode(v + 0x30) }
    );
    const letterChar = fc.mapToConstant({ num: 26, build: (v) => String.fromCharCode(v + 0x61) });

    const letters = fc.stringOf(letterChar);
    const alphanumericString = fc.stringOf(alphanumericChar);

    const prometheusMetricArbitrary = fc.record({ start: letters, rest: alphanumericString }).map(({ start, rest }) => {
      if (!/^[a-z|A-Z]+$/.test(start)) {
        throw new Error(`start is messed up: ${start}`);
      }
      if (!/^[a-z|A-Z|0-9]+$/.test(rest)) {
        throw new Error(`rest is messed up: ${rest}`);
      }
      return `${start}${rest}`;
    });

    fc.assert(
      fc.property(prometheusMetricArbitrary, fc.context(), (input, ctx) => {
        ctx.log(`input: ${input}, output: ${validateStatsNamespaceAndSubystem(input)}`);
        expect(validateStatsNamespaceAndSubystem(input)).toBe(true);
      })
    );
  });

but the assertions in prometheusMetricArbitrary are failing w/ empty strings generated…

[dubzzz]

If so, can I ask you to create another issue saying ‘add missing documentation for default values in jsdoc’ (or similar title) and close this one but reference it into the new one? It would make tracking easier.

[dubzzz]

Aren’t they already documented? If we check stringOf in the documentation generated from the jsdoc we have https://dubzzz.github.io/fast-check/functions/stringOf.html, leading us to https://dubzzz.github.io/fast-check/interfaces/StringSharedConstraints.html. Well the options are documented, but I should agree that I barely never document the @-defaultValue. By not documented do you talk about it (the at default)?