commit tests

tests/test_trans.py

@@ -0,0 +1,50 @@
+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 len(string[i:j]) == j - i
+            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)], ["{'{'''''''''}"])