Add hint for SABRE_HTTP_TEST_GET_LARGE_CONTENT_MAX_PEAK_MEMORY_USAGE …

…env var in test

tests/HTTP/ClientTest.php

@@ -211,7 +211,8 @@ public function testSendToGetLargeContent()
 
         // Allow the peak memory usage limit to be specified externally, if needed.
         // When running this test in different environments it may be appropriate to set a different limit.
-        $maxPeakMemoryUsage = \getenv('SABRE_HTTP_TEST_GET_LARGE_CONTENT_MAX_PEAK_MEMORY_USAGE');
+        $maxPeakMemoryUsageEnvVariable = 'SABRE_HTTP_TEST_GET_LARGE_CONTENT_MAX_PEAK_MEMORY_USAGE';
+        $maxPeakMemoryUsage = \getenv($maxPeakMemoryUsageEnvVariable);
         if (false === $maxPeakMemoryUsage) {
             $maxPeakMemoryUsage = 60 * pow(1024, 2);
         }
@@ -221,7 +222,11 @@ public function testSendToGetLargeContent()
         $response = $client->send($request);
 
         $this->assertEquals(200, $response->getStatus());
-        $this->assertLessThan((int) $maxPeakMemoryUsage, memory_get_peak_usage());
+        $this->assertLessThan(
+            (int) $maxPeakMemoryUsage,
+            memory_get_peak_usage(),
+            "Hint: you can adjust the max peak memory usage allowed for this test by defining env variable $maxPeakMemoryUsageEnvVariable to be the desired max bytes"
+        );
     }
 
     /**