Improved attachment retrieval and added test cases

tests/OfflineTests/ObjectRetrieverMockTest.php

@@ -115,6 +115,35 @@ class ObjectRetrieverMockTest extends \PHPUnit\Framework\TestCase {
         $this->assertNull($content);
     }
 
+    public function testWhenAPIThrowsErrorForAttachment() {
+        $this->setMockResponse(
+            new Response(200, ['Content-Type' => 'application/ld+json'],
+                '{"@id":"coid://cloudobjects.io/Test","coid://cloudobjects.io/isAtRevision":"1-abc"}'),
+            new Response(500)
+        );
+
+        $this->expectException(CoreAPIException::class);
+        $this->retriever->getAttachment(new IRI('coid://cloudobjects.io/Test'), 'file.txt');
+    }
+
+    public function testWhenAPITimesOutForAttachment() {
+        $this->setMockResponse(
+            new Response(200, ['Content-Type' => 'application/ld+json'],
+                '{"@id":"coid://cloudobjects.io/Test","coid://cloudobjects.io/isAtRevision":"1-abc"}'),
+            new ConnectException(
+                'cURL error 28: Operation timed out',
+                new Request('GET', 'cloudobjects.io')
+            )
+        );
+
+        try {
+            $this->retriever->getAttachment(new IRI('coid://cloudobjects.io/Test'), 'file.txt');
+            $this->fail('Expected CoreAPIException was not thrown.');
+        } catch (CoreAPIException $e) {
+            $this->assertInstanceOf(ConnectException::class, $e->getPrevious());
+        }
+    }
+
     private function createFallbackStoreDirectory() : string {
         $directory = sys_get_temp_dir().DIRECTORY_SEPARATOR.'clobj-fallback-'.uniqid();
         mkdir($directory);