fix(api): enforce mutual exclusivity between data and form options

playwright/_impl/_fetch.py

@@ -369,7 +369,9 @@ async def _inner_fetch(
         if self._close_reason:
             raise TargetClosedError(self._close_reason)
         assert (
-            (1 if data else 0) + (1 if form else 0) + (1 if multipart else 0)
+            (1 if data is not None else 0)
+            + (1 if form is not None else 0)
+            + (1 if multipart is not None else 0)
         ) <= 1, "Only one of 'data', 'form' or 'multipart' can be specified"
         assert (
             maxRedirects is None or maxRedirects >= 0

tests/async/test_fetch_global.py

@@ -474,6 +474,22 @@ async def test_should_serialize_request_data(
     await request.dispose()
 
 
+async def test_should_reject_empty_data_with_form(
+    playwright: Playwright, server: Server
+) -> None:
+    request = await playwright.request.new_context()
+    with pytest.raises(
+        AssertionError,
+        match="Only one of 'data', 'form' or 'multipart' can be specified",
+    ):
+        await request.post(
+            server.EMPTY_PAGE,
+            data="",
+            form={"name": "value"},
+        )
+    await request.dispose()
+
+
 async def test_should_retry_ECONNRESET(playwright: Playwright, server: Server) -> None:
     request_count = 0
 

tests/sync/test_fetch_global.py

@@ -334,6 +334,22 @@ def test_should_serialize_null_values_in_json(
     request.dispose()
 
 
+def test_should_reject_empty_data_with_form(
+    playwright: Playwright, server: Server
+) -> None:
+    request = playwright.request.new_context()
+    with pytest.raises(
+        AssertionError,
+        match="Only one of 'data', 'form' or 'multipart' can be specified",
+    ):
+        request.post(
+            server.EMPTY_PAGE,
+            data="",
+            form={"name": "value"},
+        )
+    request.dispose()
+
+
 def test_should_throw_when_fail_on_status_code_is_true(
     playwright: Playwright, server: Server
 ) -> None: