falcor-observable/test/filter-test.js

An Observable implementation compatible with the Falcor DataSource API. Avoids try/catch.

// @flow
"use strict";
const { Observable } = require("../src/es-observable");
const { expect } = require("chai");
const { spy, stub } = require("sinon");
const { filter } = require("../src");

describe("filter operator", function() {
  it("filters values", function() {
    const observable = Observable.of(0, 1, 2);
    const observer = {
      next: stub(),
      error: stub(),
      complete: stub()
    };
    const predicate = spy((value, index) => value % 2 === 0);
    filter(predicate)(observable).subscribe(observer);

    expect(predicate.args).to.deep.equal([[0, 0], [1, 1], [2, 2]]);
    expect(observer.next.args).to.deep.equal([[0], [2]]);
    expect(observer.error.called).equal(false);
    expect(observer.complete.calledOnce).equal(true);
  });

  it("preserves errors", function() {
    const err = new Error("My error");
    const observable = Observable.throw(err);
    const observer = {
      next: stub(),
      error: stub(),
      complete: stub()
    };
    filter(() => true)(observable).subscribe(observer);

    expect(observer.error.args).to.deep.equal([[err]]);
    expect(observer.next.called).equal(false);
    expect(observer.complete.called).equal(false);
  });
});