Fixes #3630

src/_pytest/logging.py

@@ -392,7 +392,9 @@ class LoggingPlugin(object):
                 config, "log_file_date_format", "log_date_format"
             )
             # Each pytest runtests session will write to a clean logfile
-            self.log_file_handler = logging.FileHandler(log_file, mode="w")
+            self.log_file_handler = logging.FileHandler(
+                log_file, mode="w", encoding="UTF-8"
+            )
             log_file_formatter = logging.Formatter(
                 log_file_format, datefmt=log_file_date_format
             )

testing/logging/test_reporting.py

@@ -827,6 +827,40 @@ def test_log_file_ini_level(testdir):
         assert "This log message won't be shown" not in contents
 
 
+def test_log_file_unicode(testdir):
+    log_file = testdir.tmpdir.join("pytest.log").strpath
+
+    testdir.makeini(
+        """
+        [pytest]
+        log_file={}
+        log_file_level = INFO
+        """.format(
+            log_file
+        )
+    )
+    testdir.makepyfile(
+        """
+        import logging
+        def test_log_file():
+            logging.getLogger('catchlog').info("Normal message")
+            logging.getLogger('catchlog').info("\u251c")
+            logging.getLogger('catchlog').info("Another normal message")
+    """
+    )
+
+    result = testdir.runpytest()
+
+    # make sure that that we get a '0' exit code for the testsuite
+    assert result.ret == 0
+    assert os.path.isfile(log_file)
+    with open(log_file, encoding="utf-8") as rfh:
+        contents = rfh.read()
+        assert "Normal message" in contents
+        assert "\u251c" in contents
+        assert "Another normal message" in contents
+
+
 @pytest.mark.parametrize("has_capture_manager", [True, False])
 def test_live_logging_suspends_capture(has_capture_manager, request):
     """Test that capture manager is suspended when we emitting messages for live logging.