add toBeIn

src/Expectation.php

@@ -371,6 +371,16 @@ final class Expectation
         return $this;
     }
 
+    /**
+     * Asserts that the value is one of the given values.
+     */
+    public function toBeIn(array $possibleValues): Expectation
+    {
+        Assert::assertContains($this->value, $possibleValues);
+
+        return $this;
+    }
+
     /**
      * Asserts that the value is infinite.
      */

tests/Features/Expect/toBeIn.php

@@ -0,0 +1,11 @@
+<?php
+
+use PHPUnit\Framework\ExpectationFailedException;
+
+test('passes', function () {
+    expect('a')->toBeIn(['a', 'b', 'c']);
+});
+
+test('failures', function () {
+    expect('d')->toBeIn(['a', 'b', 'c']);
+})->throws(ExpectationFailedException::class);