Added/Updated tests\bugs\gh_7600_test.py: Checked on 6.0.0.65 - all fine.

tests/bugs/gh_7600_test.py

@@ -0,0 +1,59 @@
+#coding:utf-8
+
+"""
+ID:          issue-7600
+ISSUE:       https://github.com/FirebirdSQL/firebird/issues/7600
+TITLE:       CASE statement different result compared to FB 2.5.9
+DESCRIPTION:
+NOTES:
+    [02.10.2023] pzotov
+    Confirmed bug on 4.0.4.2998, 5.0.0.1235.
+    Checked on 6.0.0.65 - all fine.
+"""
+
+import pytest
+from firebird.qa import *
+
+db = db_factory()
+
+test_script = """
+    set heading off;
+    select replace(
+           case when 'N' = 'Y' then cast('YES' as varchar(30)) 
+                when 'N' = 'N' then 'NO' 
+                else 'DUNNO' 
+           end,
+           ' ', '_') as test
+    from rdb$database;
+
+    select replace(
+           case when 'N' = 'Y' then cast('YES' as varchar(30)) 
+                when 'N' = 'X' then 'XXX' 
+                when 'N' = 'N' then 'NO' 
+           end,
+           ' ', '_') as test
+      from rdb$database;
+
+    select replace(
+           case 'N'
+              when 'Y' then 'YES' 
+              when 'X' then 'XXX' 
+              when 'N' then 'NO' 
+           end,
+           ' ', '_') as test
+      from rdb$database;
+"""
+
+act = isql_act('db', test_script)
+
+expected_stdout = """
+    NO
+    NO
+    NO
+"""
+
+@pytest.mark.version('>=3.0')
+def test_1(act: Action):
+    act.expected_stdout = expected_stdout
+    act.execute()
+    assert act.clean_stdout == act.clean_expected_stdout