http://edgecase.net/articles/bitcoin_transaction_test_set_2
This article contains 16 Bitcoin transactions, with 1-3 inputs and 1-3 outputs.
All transactions are onchain - and thereby confirmed to be completely valid (there is no higher level of validation). You can take each txid and look it up in a block explorer.
Private keys are included. All addresses are Pay-To-Public-Key-Hash (P2PKH).
I published it on 2020-12-19.
A Bitcoin transaction is a complicated object. Getting one of its aspects wrong can produce a transaction that looks plausible but is invalid, or worse, valid in a way the developer did not intend.
The value of a test set like this is that it gives a developer something fixed and confirmed-true to compare against. You can run your code against known cases and check whether it produces the expected transaction IDs, signatures, serialized bytes, or decoded fields.