test/cql-pytest: test confirming that casting to counter doesn't work

In the previous patch we implemented CAST operations from the COUNTER
type to various other types. We did not implement the reverse cast,
from different types to the counter type. Should we? In this patch
we add a test that shows we don't need to bother - Cassandra does not
support such casts, so it's fine that we don't too - and indeed the
test shows we don't support them.
It's not a useful operation anyway.

Signed-off-by: Nadav Har'El <nyh@scylladb.com>

test/cql-pytest/test_cast_data.py

@@ -33,6 +33,11 @@ def table2(cql, test_keyspace):
     with new_test_table(cql, test_keyspace, "p int PRIMARY KEY, c counter") as table:
         yield table
 
+@pytest.fixture(scope="module")
+def table3(cql, test_keyspace):
+    with new_test_table(cql, test_keyspace, "p int PRIMARY KEY, i int, a ascii, bi bigint, b blob, bool boolean, d date, dec decimal, db double, dur duration, f float, addr inet, si smallint, t text, tim time, ts timestamp, tu timeuuid, ti tinyint, u uuid, vc varchar, vi varint") as table:
+        yield table
+
 # Utility function for emulating a wrapping cast of a big positive number
 # into a smaller signed integer of given number of bits. For example,
 # casting 511 to 8 bits results in -1.
@@ -134,4 +139,16 @@ def test_cast_from_counter_to_varchar(cql, table2, cassandra_bug):
     cql.execute(f'UPDATE {table2} SET c = c + 1000 WHERE p = {p}')
     assert [("1000",)] == list(cql.execute(f"SELECT CAST(c AS varchar) FROM {table2} WHERE p={p}"))
 
+# Test casts from various types *to* counter type. This is a rather silly
+# operation - casting to "counter" doesn't make a real counter. It could
+# have been supported the same as casting to bigint, but Cassandra chose not
+# to support it and neither do we.
+# The only case that works is the do-nothing casting of a counter to counter,
+# and that case is already checked in test_cast_from_counter().
+def test_cast_to_counter(cql, table3):
+    p = unique_key_int()
+    for col in ['i', 'a', 'bi', 'b', 'bool', 'd', 'dec', 'db', 'dur', 'f', 'addr', 'si', 't', 'tim', 'ts', 'tu', 'ti', 'u', 'vc', 'vi']:
+        with pytest.raises(InvalidRequest, match='cannot be cast'):
+            cql.execute(f"SELECT CAST({col} AS counter) FROM {table3} WHERE p={p}")
+
 # TODO: test casts from more types.