feat: move Expectations API out of external plugin

tests/Features/Expect/toBeResource.php

@@ -0,0 +1,22 @@
+<?php
+
+use PHPUnit\Framework\ExpectationFailedException;
+
+$resource = tmpfile();
+
+afterAll(function () use ($resource) {
+    fclose($resource);
+});
+
+test('pass', function () use ($resource) {
+    expect($resource)->toBeResource();
+    expect(null)->not->toBeResource();
+});
+
+test('failures', function () {
+    expect(null)->toBeResource();
+})->throws(ExpectationFailedException::class);
+
+test('not failures', function () use ($resource) {
+    expect($resource)->not->toBeResource();
+})->throws(ExpectationFailedException::class);