feat(expect): add more methods

tests/Expect/thatDirectoryExists.php

@@ -0,0 +1,17 @@
+<?php
+
+use PHPUnit\Framework\ExpectationFailedException;
+
+test('pass', function () {
+    $temp = sys_get_temp_dir();
+
+    expect($temp)->toBeExistingDirectory();
+});
+
+test('failures', function () {
+    expect('/random/path/whatever')->toBeExistingDirectory();
+})->throws(ExpectationFailedException::class);
+
+test('not failures', function () {
+    expect('.')->not->toBeExistingDirectory();
+})->throws(ExpectationFailedException::class);