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var {all, compose , difference , equals , head , identity , is , isEmpty , length , uniq , unnest , collectBy} = require('../source');var {property} = require('jsverify');var {spy} = require('sinon');
describe('collectBy', function() {
  property('returns a list of lists', '[nat]', function(xs) {    var check = all(is(Array));    var ys = collectBy(identity)(xs);    return check(ys);  });
  property('groups items but neiter adds new ones nor removes any', '[nat]', function(xs) {    var check = compose(isEmpty, difference(xs), unnest);    var ys = collectBy(identity)(xs);    return check(ys);  });
  property('groups related items together', '[bool]', function(xs) {    var ys = collectBy(identity)(xs);    var check = all(compose(equals(1), length, uniq));    return check(ys);  });
  property('invokes the tag function for each item in the list', '[nat]', function(xs) {    var id = spy(x => 42);    collectBy(id)(xs);    var check = compose(isEmpty, difference(xs));    return check(id.getCalls().map(call => call.args[0]));  });
  property('groups items according to the tag value', '[nat]', function(xs) {    var ys = collectBy(x => 42)(xs);    var check = compose(isEmpty, difference(xs), head);    return isEmpty(xs) && isEmpty(ys) ? true : check(ys);  });});