--- /dev/null
+from typing import List, Tuple
+
+from black.trans import iter_fexpr_spans
+
+
+def test_fexpr_spans() -> None:
+ def check(
+ string: str, expected_spans: List[Tuple[int, int]], expected_slices: List[str]
+ ) -> None:
+ spans = list(iter_fexpr_spans(string))
+
+ # Checking slices isn't strictly necessary, but it's easier to verify at
+ # a glance than only spans
+ assert len(spans) == len(expected_slices)
+ for (i, j), slice in zip(spans, expected_slices):
+ assert 0 <= i <= j <= len(string)
+ assert string[i:j] == slice
+
+ assert spans == expected_spans
+
+ # Most of these test cases omit the leading 'f' and leading / closing quotes
+ # for convenience
+ # Some additional property-based tests can be found in
+ # https://github.com/psf/black/pull/2654#issuecomment-981411748
+ check("""{var}""", [(0, 5)], ["{var}"])
+ check("""f'{var}'""", [(2, 7)], ["{var}"])
+ check("""f'{1 + f() + 2 + "asdf"}'""", [(2, 24)], ["""{1 + f() + 2 + "asdf"}"""])
+ check("""text {var} text""", [(5, 10)], ["{var}"])
+ check("""text {{ {var} }} text""", [(8, 13)], ["{var}"])
+ check("""{a} {b} {c}""", [(0, 3), (4, 7), (8, 11)], ["{a}", "{b}", "{c}"])
+ check("""f'{a} {b} {c}'""", [(2, 5), (6, 9), (10, 13)], ["{a}", "{b}", "{c}"])
+ check("""{ {} }""", [(0, 6)], ["{ {} }"])
+ check("""{ {{}} }""", [(0, 8)], ["{ {{}} }"])
+ check("""{ {{{}}} }""", [(0, 10)], ["{ {{{}}} }"])
+ check("""{{ {{{}}} }}""", [(5, 7)], ["{}"])
+ check("""{{ {{{var}}} }}""", [(5, 10)], ["{var}"])
+ check("""{f"{0}"}""", [(0, 8)], ["""{f"{0}"}"""])
+ check("""{"'"}""", [(0, 5)], ["""{"'"}"""])
+ check("""{"{"}""", [(0, 5)], ["""{"{"}"""])
+ check("""{"}"}""", [(0, 5)], ["""{"}"}"""])
+ check("""{"{{"}""", [(0, 6)], ["""{"{{"}"""])
+ check("""{''' '''}""", [(0, 9)], ["""{''' '''}"""])
+ check("""{'''{'''}""", [(0, 9)], ["""{'''{'''}"""])
+ check("""{''' {'{ '''}""", [(0, 13)], ["""{''' {'{ '''}"""])
+ check(
+ '''f\'\'\'-{f"""*{f"+{f'.{x}.'}+"}*"""}-'y\\'\'\'\'''',
+ [(5, 33)],
+ ['''{f"""*{f"+{f'.{x}.'}+"}*"""}'''],
+ )
+ check(r"""{}{""", [(0, 2)], ["{}"])
+ check("""f"{'{'''''''''}\"""", [(2, 15)], ["{'{'''''''''}"])