feat(mock): support for JSON in HttpBackend

Closes #236

lib/mock/http_backend.dart

@@ -138,14 +138,23 @@ class MockHttpBackend implements HttpBackend {
     return c.future;
   }
 
-  _createResponse(status, data, headers) {
-    if (status is Function) return status;
+  _createResponse(statusOrDataOrFunction, dataOrHeaders, headersOrNone) {
+    if (statusOrDataOrFunction is Function) return statusOrDataOrFunction;
+    var status, data, headers;
+    if (statusOrDataOrFunction is num) {
+      status = statusOrDataOrFunction;
+      data = dataOrHeaders;
+      headers = headersOrNone;
+    } else {
+      status = 200;
+      data = statusOrDataOrFunction;
+      headers = dataOrHeaders;
+    }
+    if (data is Map || data is List) {
+      data = JSON.encode(data);
+    }
 
-    return ([a,b,c,d,e]) {
-      return status is num
-          ? [status, data, headers]
-          : [200, status, data];
-    };
+    return ([a,b,c,d,e]) => [status, data, headers];
   }
 
 

test/mock/http_backend_spec.dart

@@ -42,6 +42,23 @@ main() => describe('MockHttpBackend', () {
   });
 
 
+  it('should respond with JSON', inject((Logger logger) {
+    hb.when('GET', '/url1').respond(200, ['abc'], {});
+    hb.when('GET', '/url2').respond(200, {'key': 'value'}, {});
+
+
+    callback.andCallFake((status, response) {
+      expect(status).toBe(200);
+      logger(response);
+    });
+
+    hb('GET', '/url1', null, callback);
+    hb('GET', '/url2', null, callback);
+    hb.flush();
+    expect(logger).toEqual(['["abc"]', '{"key":"value"}']);
+  }));
+
+
   it('should throw error when unexpected request', () {
     hb.when('GET', '/url1').respond(200, 'content');
     expect(() {