How to rollback, reset, or drop Ecto test database?

You can access the test database by using MIX_ENV=test followed by a command such as mix do ecto.drop, mix ecto.reset or mix ecto.rollback.

In this particular case, I used:

MIX_ENV=test mix ecto.reset

If your application has multiple repos (DBs), you'll want to specify a specific repo to avoid applying the operation to all repos. For example

mix ecto.drop --repo Order.Repo

To find out more about an Ecto task, use mix help <task>

You can set aliases into mix.exs like this

defp aliases do
  [
   "ecto.setup": ["ecto.create", "ecto.migrate", "run priv/repo/seeds.exs"],
   "ecto.reset": ["ecto.drop", "ecto.setup"],
   "test":       ["ecto.create --quiet", "ecto.migrate", "test"]
  ]
end

And you need to run database into sandbox mode.

Your /appdir/test/test_helper.exs should be like this

Ecto.Adapters.SQL.Sandbox.mode(ProjectName.DB.Repo, {:shared, self()})
ExUnit.start(exclude: [:pending])

And /appdir/config/test.exs like this

config :project_name, ProjectName.DB.Repo,
  pool: Ecto.Adapters.SQL.Sandbox,
  database: "database_name_test"