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Pure Functional HTTP APIs in Scala

Integration Tests

Explore how to write integration tests for Scala HTTP API services, focusing on pure functional programming. Understand testing techniques for FlywayDatabaseMigrator and repository implementations using Doobie, and how to verify database operations effectively.

We'll cover the following...

Testing the FlywayDatabaseMigrator

To verify the basic behavior of our FlywayDatabaseMigrator, we write a simple test.

Scala
"thedatabaseisnotavailable"must{
  "throw an exception" in {
    val cfg = DatabaseConfig(
      driver = "This is no driver name!",
      url = "jdbc://some.host/whatever",
      user = "no-user",
      pass = "no-password"
    )
    val migrator: DatabaseMigrator[IO] = new FlywayDatabaseMigrator
    val program = migrator.migrate(cfg.url, cfg.user, cfg.pass)
    an[FlywayException] must be thrownBy program.unsafeRunSync
  }
}

We construct an invalid database configuration within this test and expect that the call to migrate throws an exception. Review lines 3–8. If you remember, we had this issue already and chose not to handle any exceptions but let the calling site do this, for example, via a MonadError instance.

Scala
dbConfig.map { cfg =>
    val migrator: DatabaseMigrator[IO] = new FlywayDatabaseMigrator
    val program = migrator.migrate(cfg.url, cfg.user, cfg.pass)
    program.unsafeRunSync must be > 0
}
// --
dbConfig.map { cfg =>
    val migrator: DatabaseMigrator[IO] = new FlywayDatabaseMigrator
    val program = migrator.migrate(cfg.url, cfg.user, cfg.pass)
    val _ = program.unsafeRunSync
    program.unsafeRunSync must be(0)
}

The other two tests are also quite simple: we just expect them to return either zero or the ...