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

describe(canAppear, () => {
  let enemy = {};
  let environment = {};

  describe('when it is sunny', () => {
    beforeEach(() => {
      environment.isSunny = true;
    });

    describe('and the enemy is a vampire', () => {
      beforeEach(() => {
        enemy.isVampire = true;
      });

      it('is false', () => {
        expect(canAppear(enemy, environment)).toEqual(false);
      });

      describe('and the enemy has not appeared in an hour', () => {
        beforeEach(() => {
          enemy.hasntAppearedInAnHour = true;
        });

        it('is true', () => {
          expect(canAppear(enemy, environment)).toEqual(true);
        });
      });
    });

    describe('and the enemy is not a vampire', () => {
      beforeEach(() => {
        enemy.isVampire = false;
      });

      it('is true', () => {
        expect(canAppear(enemy, environment)).toEqual(true);
      });

      describe('and the enemy has not appeared in an hour', () => {
        beforeEach(() => {
          enemy.hasntAppearedInAnHour = true;
        });

        it('is true', () => {
          expect(canAppear(enemy, environment)).toEqual(true);
        });
      });
    });
  });
});