Split out test for token in f string for py312

See gristlabs/asttokens#109 for example of
Python 3.12's change.

tests/helpers/test_get_first_token.py

@@ -1,3 +1,5 @@
+import sys
+
 import pytest
 from asttokens.util import Token
 
@@ -10,7 +12,7 @@ def f():
     do_thing()
 ''',
 ])
-def test(first_node_with_tokens):
+def test(first_node_with_tokens) -> None:
     result = get_first_token(first_node_with_tokens)
 
     assert isinstance(result, Token)
@@ -25,13 +27,39 @@ def test(first_node_with_tokens):
         ('''
 r'hello world'
 ''', 'r\'hello world\''),
-        ('''
-f"hello world"
-''', 'f"hello world"'),
     ]
 )
-def test_strings(first_node_with_tokens, expected):
+def test_strings(first_node_with_tokens, expected: str) -> None:
     result = get_first_token(first_node_with_tokens)
 
     assert isinstance(result, Token)
     assert result.string == expected
+
+
+@pytest.mark.skipif(sys.version_info >= (3, 12), reason='Requires Python 3.11 or lower')
+@pytest.mark.parametrize('code_str', ['''
+f"hello world"
+'''])
+def test_f_string(first_node_with_tokens) -> None:
+    result = get_first_token(first_node_with_tokens)
+
+    assert isinstance(result, Token)
+    assert result.string == 'f"hello world"'
+
+
+@pytest.mark.skipif(sys.version_info < (3, 12), reason="Requires Python 3.12 or higher")
+@pytest.mark.parametrize('code_str', ['''
+f"hello world"
+'''])
+def test_f_string_tokens(first_node_with_tokens, expected: str) -> None:
+    """
+    Python 3.12 has tokens for f-strings, where previous versions didn't.
+
+    This test added while upgrading to py312, but there were no integration
+    tests that this affected, just internal checks. More info on the f-string
+    change: https://github.com/gristlabs/asttokens/issues/109
+    """
+    result = get_first_token(first_node_with_tokens)
+
+    assert isinstance(result, Token)
+    assert result.string == 'f"'  # FSTRING_START token