diff --git a/httprunner/loader/check.py b/httprunner/loader/check.py
index c899634a..d428b75e 100644
--- a/httprunner/loader/check.py
+++ b/httprunner/loader/check.py
@@ -17,7 +17,7 @@ class JsonSchemaChecker(object):
             Api.parse_obj(content)
         except ValidationError as ex:
             logger.error(ex)
-            raise exceptions.FileFormatError
+            raise exceptions.FileFormatError(ex)
 
     @staticmethod
     def validate_testcase_format(content):
@@ -27,7 +27,7 @@ class JsonSchemaChecker(object):
             TestCase.parse_obj(content)
         except ValidationError as ex:
             logger.error(ex)
-            raise exceptions.FileFormatError
+            raise exceptions.FileFormatError(ex)
 
     @staticmethod
     def validate_testsuite_format(content):
@@ -37,7 +37,7 @@ class JsonSchemaChecker(object):
             TestSuite.parse_obj(content)
         except ValidationError as ex:
             logger.error(ex)
-            raise exceptions.FileFormatError
+            raise exceptions.FileFormatError(ex)
 
 
 def is_test_path(path):
diff --git a/httprunner/schema/__init__.py b/httprunner/schema/__init__.py
index 12be9833..6ff26ad9 100644
--- a/httprunner/schema/__init__.py
+++ b/httprunner/schema/__init__.py
@@ -1,3 +1,3 @@
 from .api import Api
-from .testcase import ProjectMeta, TestCase, TestCases
+from .testcase import ProjectMeta, TestCase
 from .testsuite import TestSuite
diff --git a/httprunner/schema/api.py b/httprunner/schema/api.py
index 48f73e38..eb7c0b5e 100644
--- a/httprunner/schema/api.py
+++ b/httprunner/schema/api.py
@@ -1,3 +1,5 @@
+from typing import Dict, Text
+
 from pydantic import BaseModel, Field
 
 from httprunner.schema import common
@@ -10,5 +12,5 @@ class Api(BaseModel):
     base_url: common.BaseUrl = ""
     setup_hooks: common.Hook = []
     teardown_hooks: common.Hook = []
-    extract: common.Extract = {}
+    extract: Dict[Text, Text] = {}
     validation: common.Validate = Field([], alias="validate")
diff --git a/httprunner/schema/common.py b/httprunner/schema/common.py
index c146ca06..bc97e9ff 100644
--- a/httprunner/schema/common.py
+++ b/httprunner/schema/common.py
@@ -1,22 +1,21 @@
 from enum import Enum
-from typing import Dict, List, Any
+from typing import Dict, List, Any, Text
 
 from pydantic import BaseModel, HttpUrl, Field
 
-Name = str
-Url = str
+Name = Text
+Url = Text
 BaseUrl = HttpUrl
-Variables = Dict[str, Any]
-Headers = Dict[str, str]
+Variables = Dict[Text, Any]
+Headers = Dict[Text, Text]
 Verify = bool
-Hook = List[str]
-Export = List[str]
-Extract = Dict[str, str]
+Hook = List[Text]
+Export = List[Text]
 Validate = List[Dict]
-Env = Dict[str, Any]
+Env = Dict[Text, Any]
 
 
-class MethodEnum(str, Enum):
+class MethodEnum(Text, Enum):
     GET = 'GET'
     POST = 'POST'
     PUT = "PUT"
@@ -52,10 +51,10 @@ class TestsConfig(BaseModel):
 class Request(BaseModel):
     method: MethodEnum = MethodEnum.GET
     url: Url
-    params: Dict[str, str] = {}
+    params: Dict[Text, Text] = {}
     headers: Headers = {}
     req_json: Dict = Field({}, alias="json")
-    cookies: Dict[str, str] = {}
+    cookies: Dict[Text, Text] = {}
     timeout: int = 120
     allow_redirects: bool = True
     verify: Verify = False
diff --git a/httprunner/schema/testcase.py b/httprunner/schema/testcase.py
index 72d92287..c4aec71f 100644
--- a/httprunner/schema/testcase.py
+++ b/httprunner/schema/testcase.py
@@ -1,4 +1,4 @@
-from typing import Dict, List, Text
+from typing import Dict, List, Text, Union
 
 from pydantic import BaseModel, Field
 
@@ -13,9 +13,10 @@ class ProjectMeta(BaseModel):
 
 class TestStep(BaseModel):
     name: common.Name
-    api: str = None     # TODO: replace with FilePath
+    api: Text = None     # TODO: replace with FilePath
+    testcase: Text = None
     request: common.Request = None
-    extract: Dict[str, str] = {}
+    extract: Union[Dict[Text, Text], List[Text]] = {}
     validation: common.Validate = Field([], alias="validate")
 
 
@@ -81,6 +82,3 @@ class TestCase(BaseModel):
                 }
             ]
         }
-
-
-TestCases = List[TestCase]
diff --git a/httprunner/schema/testsuite.py b/httprunner/schema/testsuite.py
index 841479fb..f973824a 100644
--- a/httprunner/schema/testsuite.py
+++ b/httprunner/schema/testsuite.py
@@ -1,8 +1,15 @@
-from typing import List
+from typing import List, Text
 
 from pydantic import BaseModel
 
-from httprunner.schema import common, TestCase
+from httprunner.schema import common
+
+
+class TestCase(BaseModel):
+    name: common.Name
+    testcase: Text
+    weight: int = 1
+    variables: common.Variables = {}
 
 
 class TestSuite(BaseModel):
diff --git a/tests/locust_tests/demo_locusts.yml b/tests/locust_tests/demo_locusts.yml
index 62ab8d69..2ec2d342 100644
--- a/tests/locust_tests/demo_locusts.yml
+++ b/tests/locust_tests/demo_locusts.yml
@@ -1,7 +1,7 @@
 config:
     name: create users with uid
     variables:
-        - device_sn: ${gen_random_string(15)}
+        device_sn: ${gen_random_string(15)}
     base_url: "http://127.0.0.1:5000"
 
 testcases: