Major fixes and new features

venv/lib/python3.12/site-packages/mypy/test/testerrorstream.py

@@ -0,0 +1,45 @@
+"""Tests for mypy incremental error output."""
+from __future__ import annotations
+
+from mypy import build
+from mypy.errors import CompileError
+from mypy.modulefinder import BuildSource
+from mypy.options import Options
+from mypy.test.data import DataDrivenTestCase, DataSuite
+from mypy.test.helpers import assert_string_arrays_equal
+
+
+class ErrorStreamSuite(DataSuite):
+    required_out_section = True
+    base_path = "."
+    files = ["errorstream.test"]
+
+    def run_case(self, testcase: DataDrivenTestCase) -> None:
+        test_error_stream(testcase)
+
+
+def test_error_stream(testcase: DataDrivenTestCase) -> None:
+    """Perform a single error streaming test case.
+
+    The argument contains the description of the test case.
+    """
+    options = Options()
+    options.show_traceback = True
+    options.hide_error_codes = True
+
+    logged_messages: list[str] = []
+
+    def flush_errors(msgs: list[str], serious: bool) -> None:
+        if msgs:
+            logged_messages.append("==== Errors flushed ====")
+            logged_messages.extend(msgs)
+
+    sources = [BuildSource("main", "__main__", "\n".join(testcase.input))]
+    try:
+        build.build(sources=sources, options=options, flush_errors=flush_errors)
+    except CompileError as e:
+        assert e.messages == []
+
+    assert_string_arrays_equal(
+        testcase.output, logged_messages, f"Invalid output ({testcase.file}, line {testcase.line})"
+    )