module Rails::Generators::Testing::Assertions

Consequently, assert_migration accepts the same arguments has assert_file.

assert_file "db/migrate/003_create_products.rb"

matches the migration name. For example, the call above is converted to:
This method manipulates the given path and tries to find any migration which

assert_migration "db/migrate/create_products.rb"

path relative to the configured destination:
Asserts a given migration exists. You need to supply an absolute path or a

def assert_migration(relative, *contents, &block)
  file_name = migration_file_name(relative)
  assert file_name, "Expected migration #{relative} to exist, but was not found"
  assert_file file_name, *contents, &block
end