feat(expectations): add toStartWith

src/Expectation.php

@@ -158,6 +158,16 @@ final class Expectation
         return $this;
     }
 
+    /**
+     * Asserts that the value starts with $expected.
+     */
+    public function toStartWith(string $expected): Expectation
+    {
+        Assert::assertStringStartsWith($expected, $this->value);
+
+        return $this;
+    }
+
     /**
      * Asserts that $count matches the number of elements of the value.
      */

tests/Expect/toStartWith.php

@@ -0,0 +1,15 @@
+<?php
+
+use PHPUnit\Framework\ExpectationFailedException;
+
+test('pass', function () {
+    expect('username')->toStartWith('user');
+});
+
+test('failures', function () {
+    expect('username')->toStartWith('password');
+})->throws(ExpectationFailedException::class);
+
+test('not failures', function () {
+    expect('username')->not->toStartWith('user');
+})->throws(ExpectationFailedException::class);