diff --git a/config/sets/phpunit-code-quality.php b/config/sets/phpunit-code-quality.php
index 540b41d8..935a2bf6 100644
--- a/config/sets/phpunit-code-quality.php
+++ b/config/sets/phpunit-code-quality.php
@@ -35,6 +35,7 @@
 use Rector\PHPUnit\CodeQuality\Rector\MethodCall\NarrowSingleWillReturnCallbackRector;
 use Rector\PHPUnit\CodeQuality\Rector\MethodCall\RemoveExpectAnyFromMockRector;
 use Rector\PHPUnit\CodeQuality\Rector\MethodCall\SingleWithConsecutiveToWithRector;
+use Rector\PHPUnit\CodeQuality\Rector\MethodCall\StringCastAssertStringContainsStringRector;
 use Rector\PHPUnit\CodeQuality\Rector\MethodCall\UseSpecificWillMethodRector;
 use Rector\PHPUnit\CodeQuality\Rector\MethodCall\UseSpecificWithMethodRector;
 
@@ -63,6 +64,7 @@
 
         // type declarations
         TypeWillReturnCallableArrowFunctionRector::class,
+        StringCastAssertStringContainsStringRector::class,
 
         NarrowUnusedSetUpDefinedPropertyRector::class,
 
diff --git a/rules-tests/CodeQuality/Rector/MethodCall/AssertTrueFalseToSpecificMethodRector/Fixture/fixture2.php b/rules-tests/CodeQuality/Rector/MethodCall/AssertTrueFalseToSpecificMethodRector/Fixture/fixture2.php
new file mode 100644
index 00000000..3719dcb3
--- /dev/null
+++ b/rules-tests/CodeQuality/Rector/MethodCall/AssertTrueFalseToSpecificMethodRector/Fixture/fixture2.php
@@ -0,0 +1,16 @@
+<?php
+
+namespace Rector\PHPUnit\Tests\CodeQuality\Rector\MethodCall\AssertTrueFalseToSpecificMethodRector\Fixture;
+
+use PHPUnit\Framework\TestCase;
+
+final class MyTest2 extends TestCase
+{
+    public function test()
+    {
+        $this->assertTrue(\array_search($foo, $this->bar->toArray()));
+        $this->assertNotFalse(\array_search($foo, $this->bar->toArray()));
+    }
+}
+
+?>
diff --git a/rules-tests/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector/Fixture/repeated_same.php.inc b/rules-tests/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector/Fixture/repeated_same.php.inc
new file mode 100644
index 00000000..ec61af8a
--- /dev/null
+++ b/rules-tests/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector/Fixture/repeated_same.php.inc
@@ -0,0 +1,31 @@
+<?php
+
+namespace Rector\PHPUnit\Tests\CodeQuality\Rector\MethodCall\StringCastAssertStringContainsStringRector\Fixture;
+
+use PHPUnit\Framework\TestCase;
+
+class SomeTest extends TestCase
+{
+    public function testSomething(?string $value)
+    {
+        $this->assertStringContainsString('foo', $value);
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\PHPUnit\Tests\CodeQuality\Rector\MethodCall\StringCastAssertStringContainsStringRector\Fixture;
+
+use PHPUnit\Framework\TestCase;
+
+class SomeTest extends TestCase
+{
+    public function testSomething(?string $value)
+    {
+        $this->assertStringContainsString('foo', (string) $value);
+    }
+}
+
+?>
diff --git a/rules-tests/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector/Fixture/skip_known_string.php.inc b/rules-tests/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector/Fixture/skip_known_string.php.inc
new file mode 100644
index 00000000..9c2c310b
--- /dev/null
+++ b/rules-tests/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector/Fixture/skip_known_string.php.inc
@@ -0,0 +1,13 @@
+<?php
+
+namespace Rector\PHPUnit\Tests\CodeQuality\Rector\MethodCall\StringCastAssertStringContainsStringRector\Fixture;
+
+use PHPUnit\Framework\TestCase;
+
+class SkipKnownString extends TestCase
+{
+    public function testSomething(string $value)
+    {
+        $this->assertStringContainsString('foo', $value);
+    }
+}
diff --git a/rules-tests/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector/StringCastAssertStringContainsStringRectorTest.php b/rules-tests/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector/StringCastAssertStringContainsStringRectorTest.php
new file mode 100644
index 00000000..5fbe87da
--- /dev/null
+++ b/rules-tests/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector/StringCastAssertStringContainsStringRectorTest.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\PHPUnit\Tests\CodeQuality\Rector\MethodCall\StringCastAssertStringContainsStringRector;
+
+use Iterator;
+use PHPUnit\Framework\Attributes\DataProvider;
+use Rector\Testing\PHPUnit\AbstractRectorTestCase;
+
+final class StringCastAssertStringContainsStringRectorTest extends AbstractRectorTestCase
+{
+    #[DataProvider('provideData')]
+    public function test(string $filePath): void
+    {
+        $this->doTestFile($filePath);
+    }
+
+    public static function provideData(): Iterator
+    {
+        return self::yieldFilesFromDirectory(__DIR__ . '/Fixture');
+    }
+
+    public function provideConfigFilePath(): string
+    {
+        return __DIR__ . '/config/configured_rule.php';
+    }
+}
diff --git a/rules-tests/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector/config/configured_rule.php b/rules-tests/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector/config/configured_rule.php
new file mode 100644
index 00000000..ca95627a
--- /dev/null
+++ b/rules-tests/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector/config/configured_rule.php
@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+use Rector\Config\RectorConfig;
+use Rector\PHPUnit\CodeQuality\Rector\MethodCall\StringCastAssertStringContainsStringRector;
+
+return static function (RectorConfig $rectorConfig): void {
+    $rectorConfig->rule(StringCastAssertStringContainsStringRector::class);
+};
diff --git a/rules/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector.php b/rules/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector.php
new file mode 100644
index 00000000..c59ca4b4
--- /dev/null
+++ b/rules/CodeQuality/Rector/MethodCall/StringCastAssertStringContainsStringRector.php
@@ -0,0 +1,95 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\PHPUnit\CodeQuality\Rector\MethodCall;
+
+use PhpParser\Node;
+use PhpParser\Node\Expr\Cast\String_;
+use PhpParser\Node\Expr\MethodCall;
+use PhpParser\Node\Expr\StaticCall;
+use Rector\PHPUnit\NodeAnalyzer\TestsNodeAnalyzer;
+use Rector\Rector\AbstractRector;
+use Symplify\RuleDocGenerator\ValueObject\CodeSample\CodeSample;
+use Symplify\RuleDocGenerator\ValueObject\RuleDefinition;
+
+/**
+ * @see \Rector\PHPUnit\Tests\CodeQuality\Rector\MethodCall\StringCastAssertStringContainsStringRector\StringCastAssertStringContainsStringRectorTest
+ */
+final class StringCastAssertStringContainsStringRector extends AbstractRector
+{
+    public function __construct(
+        private readonly TestsNodeAnalyzer $testsNodeAnalyzer
+    ) {
+    }
+
+    public function getRuleDefinition(): RuleDefinition
+    {
+        return new RuleDefinition(
+            'Cast 2nd argument in assertStringContainsString() to a string if not yet',
+            [
+                new CodeSample(
+                    <<<'CODE_SAMPLE'
+use PHPUnit\Framework\TestCase;
+
+class SomeTest extends TestCase
+{
+    public function testSomething(?string $value)
+    {
+        $this->assertStringContainsString('foo', $value);
+    }
+}
+CODE_SAMPLE
+                    ,
+                    <<<'CODE_SAMPLE'
+use PHPUnit\Framework\TestCase;
+
+class SomeTest extends TestCase
+{
+    public function testSomething(?string $value)
+    {
+        $this->assertStringContainsString('foo', (string) $value);
+    }
+}
+CODE_SAMPLE
+                ),
+            ]
+        );
+    }
+
+    /**
+     * @return array<class-string<MethodCall|StaticCall>>
+     */
+    public function getNodeTypes(): array
+    {
+        return [MethodCall::class, StaticCall::class];
+    }
+
+    /**
+     * @param MethodCall|StaticCall $node
+     */
+    public function refactor(Node $node): MethodCall|StaticCall|null
+    {
+        if ($node->isFirstClassCallable()) {
+            return null;
+        }
+
+        if (! $this->testsNodeAnalyzer->isPHPUnitMethodCallNames(
+            $node,
+            ['assertStringContainsString', 'assertStringNotContainsString']
+        )) {
+            return null;
+        }
+
+        $secondArg = $node->getArgs()[1];
+        $secondArgType = $this->getType($secondArg->value);
+
+        if ($secondArgType->isString()->yes()) {
+            return null;
+        }
+
+        $secondArg->value = new String_($secondArg->value);
+
+        return null;
+    }
+}