geninq/src/functions/single.test.ts

A JavaScript version of the Linq library for Generators

import { It, ItThrows } from "../test-utils";
import "./single";

ItThrows(
  "Throws if more than one matching element",
  (s) => s.single(),
  new Error("Too many matches in sequence")
);
ItThrows(
  "Throws if more than one matching element with predicate",
  (s) => s.single((i) => i !== 2),
  new Error("Too many matches in sequence")
);
It(
  "Gets the only element in a sequence that matches a predicate",
  (s) => s.single((i) => i === 2),
  2
);
It(
  "Returns undefined if the sequence is empty",
  (s) => s.single("or-default"),
  undefined,
  []
);
It(
  "Returns undefined if the element does not exist",
  (s) => s.single((i) => i === 4, "or-default"),
  undefined
);
ItThrows(
  "Throws for element that does not exist",
  (s) => s.single((i) => i === 4),
  new Error("No matching elements in sequence.")
);
ItThrows(
  "Throws for an empty sequence",
  (s) => s.single(),
  new Error("No matching elements in sequence."),
  []
);