Retrieve Blockchain events

[m-Peter]

Work towards: onflow/developer-grants#148
Companion PR: onflow/cadence#2505 ✔️

Description

Provides a way to programmatically retrieve emitted events from the Blockchain, from within the testing framework, with:

import Test

pub let blockchain = Test.newEmulatorBlockchain()

// Retrieve all events from the blockchain
pub let events = blockchain.events()

// Retrieve events from the blockchain, filtered by type
let type: Type = CompositeType("A.01cf0e2f2f715450.FooContract.NumberAdded")!
pub let specificEvents = blockchain.eventsOfType(type)

---

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• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
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[turbolent]

@m-Peter Can you try updating to the latest Cadence master in this PR and see if that fixes it?

[m-Peter]

@turbolent Sure thing, give me a few minutes to set it up 👍

[m-Peter]

@turbolent Yes, works like a charm. Now I get something like:

DBG LOG: flow.AccountContractAdded(codeHash: [93, 30, 218, 233, 148, 57, 196, 34, 191, 78, 54, 3, 253, 41, 197, 212, 65, 138, 60, 82, 151, 184, 56, 82, 34, 5, 198, 112, 25, 103, 186, 220], contract: "FUSD", address: 0xf8d6e0586b0a20c7)

The type is loaded correctly.

[turbolent]

Awesome!

[turbolent]

Nice!

[SupunS]

@m-Peter The backend here might be a problem similar to #114 (comment). e.g.: Creating two blockchains, and returning events from both.
Would be good to double-check. Maybe add a test case?

[m-Peter]

Yes, I know 😅 I was caught off-guard, I didn't think it would be merged today 😇
However, I did check the previous comment. Why do you think that it would be a problem? The backend is basically a singleton, it gets instantiated every time the import Test declaration is encountered, without actually calling Test.newEmulatorBlockchain. And the way the wiring is done in flow-cli, https://github.com/onflow/flow-cli/blob/master/internal/test/test.go#L120-L125, a new TestRunner is created per test file. Can you share a test case where a erroneous side-effect can manifest?

[m-Peter]

Oh sorry, I just saw that you wrote Maybe add a test case? 😅 I will certainly add tests.

[SupunS]

yeah, I'm also not certain whether that is actually a problem, but rather a hunch that it may potentially cause problems.

A good example/test-case would be, in the same test-script:

• Create blockchain, blockchain1.
  • Deploy a contract Foo to the blockchain1, that emits an event Foo.Event.
  • Run a script/transaction that triggers the emitting of event Foo.Event.
  • Then get all events from blockchain1.
• Create another blockchain, blockchain2.
  • Deploy a contract Bar to the blockchain2, that emits an event Bar.Event.
  • Run a script/transaction that triggers the emitting of event Bar.Event.
  • Then get all events from blockchain2.

If this works fine, I guess we should be good.

[m-Peter]

Perfect, I will add a case like that!