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/lt.test.js

@@ -0,0 +1,16 @@
+import assert from 'assert';
+import lt from '../lt.js';
+
+describe('lt', function() {
+  it('should return `true` if `value` is less than `other`', function() {
+    assert.strictEqual(lt(1, 3), true);
+    assert.strictEqual(lt('abc', 'def'), true);
+  });
+
+  it('should return `false` if `value` >= `other`', function() {
+    assert.strictEqual(lt(3, 1), false);
+    assert.strictEqual(lt(3, 3), false);
+    assert.strictEqual(lt('def', 'abc'), false);
+    assert.strictEqual(lt('def', 'def'), false);
+  });
+});