add run test

Author: BobTheBuidler

mypyc/test-data/run-strings.test

@@ -416,6 +416,11 @@ from datetime import datetime
 var = 'mypyc'
 num = 20
 
+def final_value_setter() -> str:
+    return 'hello'
+
+final_var: Final = final_value_setter()
+
 def test_fstring_basics() -> None:
     assert f'Hello {var}, this is a test' == "Hello mypyc, this is a test"
 
@@ -451,6 +456,8 @@ def test_fstring_basics() -> None:
     inf_num = float('inf')
     assert f'{nan_num}, {inf_num}' == 'nan, inf'
 
+    assert f'{final_var}' == 'hello'
+
 # F-strings would be translated into ''.join[string literals, format method call, ...] in mypy AST.
 # Currently we are using a str.join specializer for f-string speed up. We might not cover all cases
 # and the rest ones should fall back to a normal str.join method call.