Most of the small libs I've shared are mainly sharing unit tests.

Here's a function I've shared on npm:

  var kind = function(item) {
    var getPrototype = function(item) {
      return Object.prototype.toString.call(item).slice(8, -1);
    };
    var kind, Undefined;
    if (item === null ) {
      kind = 'null';
    } else {
      if ( item === Undefined ) {
        kind = 'undefined';
      } else {
        var prototype = getPrototype(item);
        if ( ( prototype === 'Number' ) && isNaN(item) ) {
          kind = 'NaN';
        } else {
          kind = prototype;
        }
      }
    }
    return kind;
  };

  suite('kind', function(){
    test('shows number-like things as numbers', function(){
      assert(avkind(37) === 'Number');
      assert(avkind(3.14) === 'Number');
      assert(avkind(Math.LN2) === 'Number');
      assert(avkind(Infinity) === 'Number');
      assert(avkind(Number(1)) === 'Number');
      assert(avkind(new Number(1)) === 'Number');
    });
    test('shows NaN as NaN', function(){
      assert(avkind(NaN) === 'NaN');
    });
    test('Shows strings as strings', function(){
      assert(avkind('') === 'String');
      assert(avkind('bla') === 'String');
      assert(avkind(String("abc")) === 'String');
      assert(avkind(new String("abc")) === 'String');
    });
    test('shows strings accurately', function(){
      assert(avkind(true) === 'Boolean');
      assert(avkind(false) === 'Boolean');
      assert(avkind(new Boolean(true)) === 'Boolean');
    });
    test('shows arrays accurately', function(){
      assert(avkind([1, 2, 4]) === 'Array');
      assert(avkind(new Array(1, 2, 3)) === 'Array');
    });
    test('shows objects accurately', function(){
      assert(avkind({a:1}) === 'Object');
      assert(avkind(new Object()) === 'Object');
    });
    test('shows dates accurately', function(){
      assert(avkind(new Date()) === 'Date');
    });
    test('loves Functions too', function(){
      assert(avkind(function(){}) === 'Function');
      assert(avkind(new Function("console.log(arguments)")) === 'Function');
      assert(avkind(Math.sin) === 'Function');
    });
    test('shows undefined accurately', function(){
      assert(avkind(undefined) === 'undefined');
    });
    test('shows null accurately', function(){
      assert(avkind(null) === 'null');
    });
  });