introducing toBeDigits

src/Mixins/Expectation.php

@@ -502,6 +502,18 @@ final class Expectation
         return $this;
     }
 
+    /**
+     * Asserts that the value contains only digits.
+     *
+     * @return self<TValue>
+     */
+    public function toBeDigits(string $message = ''): self
+    {
+        Assert::assertTrue(ctype_digit((string) $this->value), $message);
+
+        return $this;
+    }
+
     /**
      * Asserts that the value is of type object.
      *

tests/Features/Expect/toBeDigits.php

@@ -0,0 +1,20 @@
+<?php
+
+use PHPUnit\Framework\ExpectationFailedException;
+
+test('pass', function () {
+    expect('123')->toBeDigits();
+    expect('123.14')->not->toBeDigits();
+});
+
+test('failures', function () {
+    expect('123.14')->toBeDigits();
+})->throws(ExpectationFailedException::class);
+
+test('failures with custom message', function () {
+    expect('123.14')->toBeDigits('oh no!');
+})->throws(ExpectationFailedException::class, 'oh no!');
+
+test('not failures', function () {
+    expect('445')->not->toBeDigits();
+})->throws(ExpectationFailedException::class);