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/isIterateeCall.js

@@ -0,0 +1,47 @@
+import assert from 'assert';
+import { MAX_SAFE_INTEGER } from './utils.js';
+import _isIterateeCall from '../.internal/isIterateeCall.js';
+
+describe('isIterateeCall', function() {
+  var array = [1],
+      func = _isIterateeCall,
+      object =  { 'a': 1 };
+
+  it('should return `true` for iteratee calls', function() {
+    function Foo() {}
+    Foo.prototype.a = 1;
+
+    if (func) {
+      assert.strictEqual(func(1, 0, array), true);
+      assert.strictEqual(func(1, 'a', object), true);
+      assert.strictEqual(func(1, 'a', new Foo), true);
+    }
+  });
+
+  it('should return `false` for non-iteratee calls', function() {
+    if (func) {
+      assert.strictEqual(func(2, 0, array), false);
+      assert.strictEqual(func(1, 1.1, array), false);
+      assert.strictEqual(func(1, 0, { 'length': MAX_SAFE_INTEGER + 1 }), false);
+      assert.strictEqual(func(1, 'b', object), false);
+    }
+  });
+
+  it('should work with `NaN` values', function() {
+    if (func) {
+      assert.strictEqual(func(NaN, 0, [NaN]), true);
+      assert.strictEqual(func(NaN, 'a', { 'a': NaN }), true);
+    }
+  });
+
+  it('should not error when `index` is an object without a `toString` method', function() {
+    if (func) {
+      try {
+        var actual = func(1, { 'toString': null }, [1]);
+      } catch (e) {
+        var message = e.message;
+      }
+      assert.strictEqual(actual, false, message || '');
+    }
+  });
+});