MigrationTestHelper

open class MigrationTestHelper : TestWatcher

androidx.room.testing.MigrationTestHelper

A class that can be used in your Instrumentation tests that can create the database in an older schema.

You must copy the schema json files (created by passing room.schemaLocation argument into the annotation processor) into your test assets and pass in the path for that folder into the constructor. This class will read the folder and extract the schemas from there.

 android { defaultConfig { javaCompileOptions { annotationProcessorOptions { arguments = ["room.schemaLocation": "$projectDir/schemas".toString()] } } } sourceSets { androidTest.assets.srcDirs += files("$projectDir/schemas".toString()) } }

Summary

Public constructors
`<init>(instrumentation: Instrumentation!, assetsFolder: String!)` Creates a new migration helper.
`<init>(instrumentation: Instrumentation!, assetsFolder: String!, openFactory: SupportSQLiteOpenHelper.Factory!)` Creates a new migration helper.

Public methods
open SupportSQLiteDatabase!	`createDatabase(name: String!, version: Int)` Creates the database in the given version.
open Unit	`closeWhenFinished(db: SupportSQLiteDatabase!)` Registers a database connection to be automatically closed when the test finishes.
open Unit	`closeWhenFinished(db: RoomDatabase!)` Registers a database connection to be automatically closed when the test finishes.
open SupportSQLiteDatabase!	`runMigrationsAndValidate(name: String!, version: Int, validateDroppedTables: Boolean, vararg migrations: Migration!)` Runs the given set of migrations on the provided database.

Protected methods
open Unit	`finished(description: Description!)`
open Unit	`starting(description: Description!)`

Public constructors

<init>

MigrationTestHelper(instrumentation: Instrumentation!, assetsFolder: String!)

Creates a new migration helper. It uses the Instrumentation context to load the schema (falls back to the app resources) and the target context to create the database.

Parameters
`instrumentation`	Instrumentation!: The instrumentation instance.
`assetsFolder`	Instrumentation!: The asset folder in the assets directory.

<init>

MigrationTestHelper(instrumentation: Instrumentation!, assetsFolder: String!, openFactory: SupportSQLiteOpenHelper.Factory!)

Creates a new migration helper. It uses the Instrumentation context to load the schema (falls back to the app resources) and the target context to create the database.

Parameters
`instrumentation`	Instrumentation!: The instrumentation instance.
`assetsFolder`	Instrumentation!: The asset folder in the assets directory.
`openFactory`	Instrumentation!: Factory class that allows creation of `SupportSQLiteOpenHelper`

Public methods

createDatabase

open fun createDatabase(name: String!, version: Int): SupportSQLiteDatabase!

Creates the database in the given version. If the database file already exists, it tries to delete it first. If delete fails, throws an exception.

Parameters
`name`	String!: The name of the database.
`version`	String!: The version in which the database should be created.

Return
SupportSQLiteDatabase!: A database connection which has the schema in the requested version.

Exceptions
`IOException`	If it cannot find the schema description in the assets folder.

closeWhenFinished

open fun closeWhenFinished(db: SupportSQLiteDatabase!): Unit

Registers a database connection to be automatically closed when the test finishes.

This only works if MigrationTestHelper is registered as a Junit test rule via Rule annotation.

Parameters
`db`	SupportSQLiteDatabase!: The database connection that should be closed after the test finishes.

closeWhenFinished

open fun closeWhenFinished(db: RoomDatabase!): Unit

Registers a database connection to be automatically closed when the test finishes.

This only works if MigrationTestHelper is registered as a Junit test rule via Rule annotation.

Parameters
`db`	RoomDatabase!: The RoomDatabase instance which holds the database.

runMigrationsAndValidate

open fun runMigrationsAndValidate(name: String!, version: Int, validateDroppedTables: Boolean, vararg migrations: Migration!): SupportSQLiteDatabase!

Runs the given set of migrations on the provided database.

It uses the same algorithm that Room uses to choose migrations so the migrations instances that are provided to this method must be sufficient to bring the database from current version to the desired version.

After the migration, the method validates the database schema to ensure that migration result matches the expected schema. Handling of dropped tables depends on the validateDroppedTables argument. If set to true, the verification will fail if it finds a table that is not registered in the Database. If set to false, extra tables in the database will be ignored (this is the runtime library behavior).

Parameters
`name`	String!: The database name. You must first create this database via `createDatabase(String, int)`.
`version`	String!: The final version after applying the migrations.
`validateDroppedTables`	String!: If set to true, validation will fail if the database has unknown tables.
`migrations`	String!: The list of available migrations.

Exceptions
`IOException`	If it cannot find the schema for `toVersion`.
`IllegalStateException`	If the schema validation fails.

Protected methods

finished

protected open fun finished(description: Description!): Unit

starting

protected open fun starting(description: Description!): Unit