test: add a test for #1836, by Marco Ricci

tests/test_html.py

@@ -1203,6 +1203,36 @@ def test_bug_1828(self) -> None:
             '3     ccc"]',
             ]
 
+    @pytest.mark.parametrize(
+        "leader", ["", "f", "r", "fr", "rf"],
+        ids=["string", "f-string", "raw_string", "f-raw_string", "raw_f-string"]
+    )
+    def test_bug_1836(self, leader) -> None:
+        # https://github.com/nedbat/coveragepy/issues/1836
+        self.make_file("py312_fstrings.py", f"""\
+            prog_name = 'bug.py'
+            err_msg = {leader}'''\\
+            {{prog_name}}: ERROR: This is the first line of the error.
+            {{prog_name}}: ERROR: This is the second line of the error.
+            \\
+            {{prog_name}}: ERROR: This is the third line of the error.
+            '''
+            """)
+
+        cov = coverage.Coverage()
+        py312_fstrings = self.start_import_stop(cov, "py312_fstrings")
+        cov.html_report(py312_fstrings)
+
+        assert self.get_html_report_text_lines("py312_fstrings.py") == [
+            "1" + "prog_name = 'bug.py'",
+            "2" + f"err_msg = {leader}'''\\",
+            "3" + "{prog_name}: ERROR: This is the first line of the error.",
+            "4" + "{prog_name}: ERROR: This is the second line of the error.",
+            "5" + "\\",
+            "6" + "{prog_name}: ERROR: This is the third line of the error.",
+            "7" + "'''",
+            ]
+
     def test_unicode(self) -> None:
         surrogate = "\U000e0100"