Remove incorrect argument to json_encode() and add unit test

src/Services/PreHashStrings/LegacyPreHashString.php

@@ -137,7 +137,7 @@ public function getPreHashString(
         if (in_array($this->service, static::SERVICES_REQUIRING_SIGNED_REQUEST)) {
             $requestJson = $request;
             if (is_array($request)) {
-                $requestJson = json_encode($request, true);
+                $requestJson = json_encode($request);
             }
             $signatureArray[] = $requestJson;
         }
@@ -162,6 +162,11 @@ public static function supportsService(string $service): bool
         return in_array($service, static::SUPPORTED_SERVICES);
     }
 
+    /**
+     * Validate and normalise the security and request packets.  Currently
+     * nothing is done with the request packet, but future pre-hash schemes
+     * may require it.
+     */
     public function validate(array $security, array $request): array
     {
         foreach (array_keys($security) as $key) {

tests/Services/PreHashStrings/LegacyPreHashStringTest.php

@@ -82,6 +82,46 @@ public function preHashStringProvider()
             }
         }
 
-        return $testCases;
+        return array_merge($testCases, $this->additionalTests());
+    }
+
+    /**
+     * Additional test cases that detect bugs found or anticipated.
+     * @returns array <string $name, array <
+     *  string $service
+     *  array $security
+     *  string $secret
+     *  array $request
+     *  ?string $action
+     *  bool $v1Compat
+     *  string $expected
+     * >>
+     */
+    public function additionalTests(): array
+    {
+        return [
+            'api-items-json_encode-bug' => $this->jsonEncodeBugParams(),
+        ];
+    }
+
+    /**
+     * Test case for a bug found when the request contains escapable characters.
+     * @returns array <
+     *  string $service
+     *  array $security
+     *  string $secret
+     *  array $request
+     *  ?string $action
+     *  bool $v1Compat
+     *  string $expected
+     * >
+     */
+    public function jsonEncodeBugParams(): array
+    {
+        $params = ParamsFixture::getWorkingItemsApiParams(true);
+        $params['request']['name'] = str_replace('-', '<&\'>', $params['request']['name']);
+        $params['v1Compat'] = false;
+        $params['expected'] = 'yis0TYCu7U9V4o7M_localhost_20140626-0528_$ANONYMIZED_USER_ID_{"user_id":"$ANONYMIZED_USER_ID","rendering_type":"assess","name":"' . $params['request']['name'] . '","state":"initial","activity_id":"items_assess_demo","session_id":"demo_session_uuid","type":"submit_practice","config":{"configuration":{"responsive_regions":true},"navigation":{"scrolling_indicator":true},"regions":"main","time":{"show_pause":true,"max_time":300},"title":"ItemsAPI Assess Isolation Demo","subtitle":"Testing Subtitle Text"},"items":["Demo3"]}';
+        return $params;
     }
 }