Nice, that is what I was looking for. Of course, it'd need to point to production data as well, so maybe test_case is null, in that case:

  CREATE TABLE data_a AS (SELECT 'a' AS test_case, 1 AS value);
  CREATE TABLE data_b AS (SELECT 'b' AS test_case, 2 AS value);
  CREATE TABLE data_prod AS (SELECT NULL AS test_case, prod_table.value FROM prod_table);

  CREATE VIEW data AS (SELECT * FROM data_a UNION ALL SELECT * FROM data_b UNION ALL SELECT * FROM data_prod);

  CREATE VIEW complicated_query AS (SELECT test_case, value+1 FROM data);

  -- when testing
  SELECT * FROM complicated_query WHERE test_case = 'a';
  SELECT * FROM complicated_query WHERE test_case = 'b';

  -- when in 'production'
  SELECT * FROM complicated_query WHERE test_case IS NULL;