function canAppear(enemy, environment) {
  return Boolean(
    (environment.isSunny && !enemy.isVampire) ||
      (environment.isRainy && enemy.hasWaterResistantArmor) ||
      enemy.hasntAppearedInAnHour
  );
}

describe(canAppear, () => {
  [
             [true,    false,     false,   true,                   false,                 true],
             [true,    false,     false,   true,                   true,                  true],
             [false,   false,     true,    false,                  false,                 false],
  ].forEach(([isSunny, isVampire, isRainy, hasWaterResistantArmor, hasntAppearedInAnHour, expected]) => {
    const climate =
      isSunny
        ? 'sunny'
        : isRainy
        ? 'rainy'
        : 'unknown';

    describe(`when it is a ${climate} climate`, () => {
      describe(`and the enemy is ${ isVampire ? '' : 'not ' }a vampire`, () => {
        describe(`and the enemy ${hasWaterResistantArmor ? 'has ' : 'does not have '}water resisting armor`, () => {

          describe(`and the enemy has ${hasntAppearedInAnHour ? 'not ' : ''}appeared in an hour`, () => {
            it(`is ${expected}`, () => {
              expect(
                canAppear(
                  { isVampire, hasWaterResistantArmor, hasntAppearedInAnHour },
                  { isSunny, isRainy }
                )
              )
                .toEqual(expected);
            });
          });
        });
      });
    });
  });
});