What is Konsist?

Konsist is a structural linter (static code analyzer) designed for Kotlin language. It aims to standardize the codebase by ensuring adherence to a common set of coding conventions, thereby improving the readability and maintainability of the code. It's like ArchUnit, but for Kotlin language.

The Konsist API provides developers with the capability to create custom checks through unit tests, customized to align with the project's unique requirements. Additionally, it offers smooth integration with leading testing frameworks, including JUnit4, JUnit5, and Kotest, further streamlining the development process.

Konsist tests can be executed during pull request reviews, act as safeguards to preserve the project's codebase structure and architecture. Whether you're working on Android, Spring, or Kotlin Multiplatform projects, Konsist has got you covered.

Konsist is approaching its 1.0 release, marking a significant milestone in its development journey. See the Project Status.

Konsist offers two types of checks, namely Declaration Checks and ArchitecturalChecks, to thoroughly evaluate the codebase.

Declaration Checks

The first type involves declaration checks, where custom tests are created to identify common issues and violations at the declaration level (classes, functions, properties, etc.). These cover various aspects such as class naming, package structure, visibility modifiers, presence of annotations, etc. Here are a few ideas of things to check:

• Every child class extending ViewModel must have ViewModel suffix

• Classes with the @Repository annotation should reside in ..repository.. package

• Every class constructor has alphabetically ordered parameters

• Every constructor parameter has a name derived from the class name

• Field injection and m prefix is forbidden

• Every public member in api package must be documented with KDoc

• and more...

Here is a sample test that verifies if every use case class resides in domain.usecase package:

JUnit

class UseCaseKonsistTest {
    @Test
    fun `every use case reside in use case package`() {
        Konsist
            .scopeFromProject() // Define the scope containing all Kotlin files present in the project
            .classes() // Get all class declarations
            .withNameEndingWith("UseCase") // Filter classes heaving name ending with 'UseCase'
            .assertTrue { it.resideInPackage("..domain.usecase..") } // Assert that each class resides in 'any domain.usecase any' package
    }
}

Kotest

class UseCaseKonsistTest : FreeSpec({
    "every use case reside in use case package" {
        Konsist
        .scopeFromProject() // Define the scope containing all Kotlin files present in the project
        .classes() // Get all class declarations
        .withNameEndingWith("UseCase") // Filter classes heaving name ending with 'UseCase'
        .assertTrue (
                testName = this.testCase.name.testName
         ){ 
              it.resideInPackage("..domain.usecase..") 
         } // Assert that each class resides in 'any domain.usecase any' package
    }
})

For more Konsist test samples see the Snippetssection.

ArchitecturalChecks

The second type of Konsist checks revolves around architecture boundaries - they are intended to maintain the separation of concerns between layers.

Consider this simple 3 layer of Clean Architecture:

• The domain layer is independent

• The data layer depends on domain layer

• The presentation layer depends on domain layer

• etc.

Here is a Konsist test that verifies if Clean Architecture dependency requirements are valid:

JUnit

class ArchitectureTest {
    @Test
    fun `clean architecture layers have correct dependencies`() {
        Konsist
            .scopeFromProject() // Define the scope containing all Kotlin files present in project
            .assertArchitecture { // Assert architecture
                // Define layers
                val domain = Layer("Domain", "com.myapp.domain..")
                val presentation = Layer("Presentation", "com.myapp.presentation..")
                val data = Layer("Data", "com.myapp.data..")
    
                // Define architecture assertions
                domain.dependsOnNothing()
                presentation.dependsOn(domain)
                data.dependsOn(domain)
            }
    } 
}

Kotest

class ArchitectureTest : FreeSpec({
    "every use case reside in use case package" {
        Konsist
            .scopeFromProject() // Define the scope containing all Kotlin files present in project
            .assertArchitecture { // Assert architecture
                // Define layers
                val domain = Layer("Domain", "com.myapp.domain..")
                val presentation = Layer("Presentation", "com.myapp.presentation..")
                val data = Layer("Data", "com.myapp.data..")
    
                // Define architecture assertions
                domain.dependsOnNothing()
                presentation.dependsOn(domain)
                data.dependsOn(domain)
            }
    }
})

These types of checks are useful when the architecture layer is defined by the package, rather than a module where dependencies can be enforced by the build system.

Summary

By utilizing Konsist, teams can be confident that their Kotlin codebase remains standardized and aligned with best practices, making code reviews more efficient and code maintenance smoother.