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WARNING: The lack of any code Script interpretors is currently halting this section.
8.3: Testing a Bitcoin Script
NOTE: This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning.
Bitcoin Scripting allows for considerable new control over Bitcoin transactions, but it's all somewhat abstract. How do you actually turn that theoretical Bitcoin Script into functional Bitcoin code? The first answer is to test it.
Get the Code Right
The object of testing your Bitcoin Scripts is to get the code right. Don't worry about the whole rigamarole of P2SH scripting (yet). Just worry about producing the Bitcoin Script code itself and making sure it runs and does what you expect.
This is a critically important aspect of any Bitcoin Scripting, because there's no other check on your Script. Bitcoin will often protect you from trying to send bad transactions, but it won't protect you from writing bad locking scripts. That's because the P2SH methodology actually keeps Bitcoin from knowing about the actual Script until it tries to unlock it ... and if your script doesn't run at that point, your funds are gone.
So the onus is on you to get that code right.
Retrieve Public Keys & Signatures
Most of the Bitcoin code that you're testing will be simple operators. However, you'll also need have some Bitcoin addresses, public keys, and signatures to play with. Here's a quick reminder on how to retrieve this information:
Create an address:
$ address=$(bitcoin-cli getnewaddress)
$ echo $address
mxwLPpo2X1VXXAiLHNVb55H4JASeLMDm7A
Retrieve the public key:
$ bitcoin-cli -named validateaddress address=$address | jq -r '.pubkey'
03e9ddbea8336e53a7125e5be016411ffae4df06026fc3f947337ea08b74cb8476
Create a signature: bitcoin-cli signmessage $address "Secure" IO2w2knDwAig4eQxMnq+FwAoj3W1gCO/GMyzmuyTs3n3YADPdrIhfD9PVtBhCIkP0M+6NermgGz23qs86XT8nHs=
Test a Script Online
A few online resources exist for looking at scripts, each with some of their own quirks.
The Script Playground
Charlie Marsh has built an excellent Script Playground. Just put together your unlocking script and your locking script and run them. The Script Playground evaluates Bitcoin Script as if it were unlocking a transaction. That means that, just like Bitcoin, it does an OP_VERIFY at the end. As a result, 51 48 OP_ADD won't produce anything useful (other than a green checkmark), but you can run 51 48 OP_ADD 99 OP_EQUAL and 51 47 OP_ADD 99 OP_EQUAL and it'll tell you which of those would verify.
The Playground tries to be smart about converting constants without requiring you to messily enter them by hand as bytecode, but values over 100 don't appear to work.
Bitcoin Realism: Runs an OP_VERIFY at the end of every transaction.
Keys & Signatures: