add expectations for uppercase, lowercase, alpha and alphanumeric

tests/Features/Expect/toBeAlphaNumeric.php

@@ -0,0 +1,20 @@
+<?php
+
+use PHPUnit\Framework\ExpectationFailedException;
+
+test('pass', function () {
+    expect('abc123')->toBeAlphaNumeric();
+    expect('-')->not->toBeAlphaNumeric();
+});
+
+test('failures', function () {
+    expect('-')->toBeAlphaNumeric();
+})->throws(ExpectationFailedException::class);
+
+test('failures with custom message', function () {
+    expect('-')->toBeAlphaNumeric('oh no!');
+})->throws(ExpectationFailedException::class, 'oh no!');
+
+test('not failures', function () {
+    expect('abc123')->not->toBeAlphaNumeric();
+})->throws(ExpectationFailedException::class);