fast-check-best-practice-question.js

const fc = require("fast-check");

const capitalize = text => (text ? text[0].toUpperCase() + text.slice(1) : "");

/* works fine */

it("returns the correct string", () => {
  fc.assert(
    fc.property(fc.string(), text => {
      if (text) {
        const capitalizedText = capitalize(text);
        expect(text[0].toUpperCase()).toBe(capitalizedText[0]);
        expect(capitalizedText[0].toUpperCase()).toBe(capitalizedText[0]);
        expect(capitalizedText.slice(1)).toBe(text.slice(1));
      }
    })
  );

  expect(capitalize("kiwi.com")).toBe("Kiwi.com");
  expect(capitalize(null)).toBe("");
  expect(capitalize("")).toBe("");
});

/* `text` being null/undefined will break the test */

it("returns the correct string", () => {
  fc.assert(
    fc.property(fc.string(), text => {
      const capitalizedText = capitalize(text);
      expect(text[0].toUpperCase()).toBe(capitalizedText[0]);
      expect(capitalizedText[0].toUpperCase()).toBe(capitalizedText[0]);
      expect(capitalizedText.slice(1)).toBe(text.slice(1));
    })
  );

  expect(capitalize("kiwi.com")).toBe("Kiwi.com");
  expect(capitalize(null)).toBe("");
  expect(capitalize("")).toBe("");
});