cosmos-sdk/CODING_GUIDELINES.md

# Coding Guidelines

This document is an extension to [CONTRIBUTING](./CONTRIBUTING.md) and provides more details about the coding guidelines and requirements.

## API & Design

+ Code must be well structured:
    + packages must have a limited responsibility (different concerns can go to different packages),
    + types must be easy to compose,
    + think about maintainbility and testability.
+ "Depend upon abstractions, [not] concretions".
+ Try to limit the number of methods you are exposing. It's easier to expose something later than to hide it.
+ Take advantage of `internal` package concept.
+ Follow agreed-upon design patterns and naming conventions.
+ publicly-exposed functions are named logically, have forward-thinking arguments and return types.
+ Avoid global variables and global configurators.
+ Favor composable and extensible designs.
+ Minimize code duplication.
+ Limit third-party dependencies.

Performance:

+ Avoid unnecessary operations or memory allocations.

Security:

+ Pay proper attention to exploits involving:
    + gas usage
    + transaction verification and signatures
    + malleability
    + code must be always deterministic
+ Thread safety. If some functionality is not thread-safe, or uses something that is not thread-safe, then clearly indicate the risk on each level.

## Testing

Make sure your code is well tested:

+ Provide unit tests for every unit of your code if possible. Unit tests are expected to comprise 70%-80% of your tests.
+ Describe the test scenarios you are implementing for integration tests.
+ Create integration tests for queries and msgs.
+ Use both test cases and property / fuzzy testing. We use the [rapid](pgregory.net/rapid) Go library for property-based and fuzzy testing.
+ Do not decrease code test coverage. Explain in a PR if test coverage is decreased.

We expect tests to use `require` or `assert` rather than `t.Skip` or `t.Fail`,
unless there is a reason to do otherwise.
When testing a function under a variety of different inputs, we prefer to use
[table driven tests](https://github.com/golang/go/wiki/TableDrivenTests).
Table driven test error messages should follow the following format
`<desc>, tc #<index>, i #<index>`.
`<desc>` is an optional short description of whats failing, `tc` is the
index within the test case table that is failing, and `i` is when there
is a loop, exactly which iteration of the loop failed.
The idea is you should be able to see the
error message and figure out exactly what failed.
Here is an example check:

```go
<some table>
for tcIndex, tc := range cases {
  <some code>
  resp, err := doSomething()
  require.NoError(err)
  require.Equal(t, tc.expected, resp, "should correctly perform X")
```

## Quality Assurance

We are forming a QA team that will support the core Cosmos SDK team and collaborators by:

- Improving the Cosmos SDK QA Processes
- Improving automation in QA and testing
- Defining high-quality metrics
- Maintaining and improving testing frameworks (unit tests, integration tests, and functional tests)
- Defining test scenarios.
- Verifying user experience and defining a high quality.
    - We want to have **acceptance tests**! Document and list acceptance lists that are implemented and identify acceptance tests that are still missing.
    - Acceptance tests should be specified in `acceptance-tests` directory as Markdown files.
- Supporting other teams with testing frameworks, automation, and User Experience testing.
- Testing chain upgrades for every new breaking change.
    - Defining automated tests that assure data integrity after an update.

Desired outcomes:

- QA team works with Development Team.
- QA is happening in parallel with Core Cosmos SDK development.
- Releases are more predictable.
- QA reports. Goal is to guide with new tasks and be one of the QA measures.

As a developer, you must help the QA team by providing instructions for User Experience (UX) and functional testing.