Add initial test files from lodash v4. (#4172)

* Install test dependencies.

* Add initial test files.

These files were created using a simplistic AST manipulator using `recast` to
preserve formatting. There's bound to be a huge chunk of errors, but this serves
as a good start. QUnit was replaced with Mocha, with ES2015 imports running via
`esm`.

As far as possible, QUnit-specific syntax has been replaced with Mocha's
`describe` and `it`, while the native Node.js `assert` module is used for
assertions. Files in the `test` directory ending in `.test.js` will be treated
as test files.

* Add initial passing files to test run.

test/conforms.js

@@ -0,0 +1,15 @@
+import assert from 'assert';
+import conforms from '../conforms.js';
+
+describe('conforms', function() {
+  it('should not change behavior if `source` is modified', function() {
+    var object = { 'a': 2 },
+        source = { 'a': function(value) { return value > 1; } },
+        par = conforms(source);
+
+    assert.strictEqual(par(object), true);
+
+    source.a = function(value) { return value < 2; };
+    assert.strictEqual(par(object), true);
+  });
+});