Explanation:

To validate a custom ASIM parser output, you test that the parser's resulting table structure complies with the intended ASIM schema. In KQL, the getschema operator produces a tabular representation of the current pipeline's schema (column names, types, order). The invoke operator is then used to call a function on that tabular input. ASIM provides the helper function ASimSchemaTester(), which accepts the schema table and the target schema name and validates that the input conforms (columns exist, types match, required fields are present).
Therefore, the correct construction is to run the parser (here, Parser1), pipe its output to getschema to obtain the schema of the produced table, and then invoke ASimSchemaTester('Schema1') to perform the validation. Other options are not appropriate: evaluate is for plugins; parse extracts fields from strings rather than validate schema; and calling the tester without getschema would not pass the required schema table.
Hence, the correct command is:
Parser1 | getschema | invoke ASimSchemaTester('Schema1').