diff --git a/src/ClassScanner/ClassMap.php b/src/ClassScanner/ClassMap.php
index 4ff367d..83fde8d 100644
--- a/src/ClassScanner/ClassMap.php
+++ b/src/ClassScanner/ClassMap.php
@@ -134,8 +134,16 @@ public static function fromFile(string $filename): self
      */
     public static function fromFileHandle($fileHandle): ClassMap
     {
+        \fseek($fileHandle, 0);
         $cacheContents = \stream_get_contents($fileHandle);
+        if ($cacheContents === '') {
+            throw new \InvalidArgumentException('Cannot read empty file handle');
+        }
+
         $cacheContentsJson = \json_decode($cacheContents, true, 512, \JSON_THROW_ON_ERROR);
+        if (!$cacheContentsJson) {
+            throw new \InvalidArgumentException('Cannot parse json from file handle');
+        }
 
         $classMap = new ClassMap($cacheContentsJson['scanPaths'], $cacheContentsJson['basePath']);
 
diff --git a/tests/ClassScanner/ClassMapTest.php b/tests/ClassScanner/ClassMapTest.php
new file mode 100644
index 0000000..2dc9d81
--- /dev/null
+++ b/tests/ClassScanner/ClassMapTest.php
@@ -0,0 +1,82 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Aura\Di\ClassScanner;
+
+use Aura\Di\Fake\FakeAllAttributes;
+use Aura\Di\Fake\FakeWorkerAttribute;
+use Aura\Di\Resolver\Reflector;
+use PHPUnit\Framework\TestCase;
+
+final class ClassMapTest extends TestCase
+{
+    public function testAddRemove(): void
+    {
+        $reflector = new Reflector();
+        $attributes = [...$reflector->yieldAttributes(FakeAllAttributes::class)];
+        $spec = new ClassSpecification(FakeAllAttributes::class, FakeAllAttributes::FILE, $attributes);
+
+        $map = new ClassMap([], '/');
+        $map->addClass($spec);
+
+        $this->assertContains(FakeAllAttributes::class, $map->getClasses());
+        $this->assertContains(FakeAllAttributes::FILE, $map->getFiles());
+        $this->assertNotNull($map->getClassSpecificationFor(FakeAllAttributes::class));
+        $this->assertSame($spec, $map->getClassSpecificationFor(FakeAllAttributes::class));
+        $this->assertCount(\count($attributes), $map->getAttributeSpecifications());
+    }
+
+    public function testAttributeClass(): void
+    {
+        $reflector = new Reflector();
+        $spec1 = new ClassSpecification(
+            FakeAllAttributes::class,
+            FakeAllAttributes::FILE,
+            [...$reflector->yieldAttributes(FakeAllAttributes::class)]
+        );
+        $spec2 = new ClassSpecification(
+            FakeWorkerAttribute::class,
+            FakeWorkerAttribute::FILE,
+            [...$reflector->yieldAttributes(FakeWorkerAttribute::class)]
+        );
+
+        $map = new ClassMap([], '/');
+        $map->addClass($spec1);
+        $map->addClass($spec2);
+
+        $this->assertFalse($map->isAttributeClassFile(FakeAllAttributes::FILE));
+        $this->assertTrue($map->isAttributeClassFile(FakeWorkerAttribute::FILE));
+    }
+
+    public function testReconstituteFromFileHandle(): void
+    {
+        $reflector = new Reflector();
+        $spec1 = new ClassSpecification(
+            FakeAllAttributes::class,
+            FakeAllAttributes::FILE,
+            [...$reflector->yieldAttributes(FakeAllAttributes::class)]
+        );
+        $spec2 = new ClassSpecification(
+            FakeWorkerAttribute::class,
+            FakeWorkerAttribute::FILE,
+            [...$reflector->yieldAttributes(FakeWorkerAttribute::class)]
+        );
+
+        $stream = fopen('php://temp', 'w');
+
+        $map1 = new ClassMap([], '/');
+        $map1->addClass($spec1);
+        $map1->addClass($spec2);
+        $map1->saveToFileHandle($stream);
+
+        $map2 = ClassMap::fromFileHandle($stream);
+
+        $this->assertContains(FakeAllAttributes::class, $map2->getClasses());
+        $this->assertContains(FakeAllAttributes::FILE, $map2->getFiles());
+        $this->assertContains(FakeWorkerAttribute::class, $map2->getClasses());
+        $this->assertContains(FakeWorkerAttribute::FILE, $map2->getFiles());
+        $this->assertCount(\count($spec1->getAttributes()), $map2->getClassSpecificationFor(FakeAllAttributes::class)->getAttributes());
+        $this->assertCount(\count($spec2->getAttributes()), $map2->getClassSpecificationFor(FakeWorkerAttribute::class)->getAttributes());
+    }
+}
\ No newline at end of file
diff --git a/tests/Fake/FakeAllAttributes.php b/tests/Fake/FakeAllAttributes.php
index fbb28f3..954da3c 100644
--- a/tests/Fake/FakeAllAttributes.php
+++ b/tests/Fake/FakeAllAttributes.php
@@ -10,6 +10,8 @@ class FakeAllAttributes
     #[FakeAttribute(\Attribute::TARGET_CLASS_CONSTANT)]
     public const CONSTANT = 1;
 
+    public const FILE = __FILE__;
+
     public function __construct(
         #[FakeAttribute(\Attribute::TARGET_PARAMETER)]
         $parameter,
diff --git a/tests/Fake/FakeWorkerAttribute.php b/tests/Fake/FakeWorkerAttribute.php
index 91008b1..2b09742 100644
--- a/tests/Fake/FakeWorkerAttribute.php
+++ b/tests/Fake/FakeWorkerAttribute.php
@@ -13,6 +13,8 @@
 #[BlueprintNamespace(__NAMESPACE__)]
 class FakeWorkerAttribute implements AttributeConfigInterface
 {
+    public const FILE = __FILE__;
+
     private int $someSetting;
 
     public function __construct(int $someSetting = 1)