94 lines
3.1 KiB
Markdown
94 lines
3.1 KiB
Markdown
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# Testing migrations
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In order to reliably test a migration, we need to test it against a database
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schema that this migration has been written for. In order to achieve that we
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have some _migration helpers_ and RSpec test tag, called `:migration`.
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If you want to write a test for a migration consider adding `:migration` tag to
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the test signature, like `describe SomeMigrationClass, :migration`.
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## How does it work?
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Adding a `:migration` tag to a test signature injects a few before / after
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hooks to the test.
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The most important change is that adding a `:migration` tag adds a `before`
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hook that will revert all migrations to the point that a migration under test
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is not yet migrated.
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In other words, our custom RSpec hooks will find a previous migration, and
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migrate the database **down** to the previous migration version.
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With this approach you can test a migration against a database schema that this
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migration has been written for.
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Use `migrate!` helper to run the migration that is under test.
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The `after` hook will migrate the database **up** and reinstitutes the latest
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schema version, so that the process does not affect subsequent specs and
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ensures proper isolation.
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## Testing a class that is not an ActiveRecord::Migration
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In order to test a class that is not a migration itself, you will need to
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manually provide a required schema version. Please add a `schema` tag to a
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context that you want to switch the database schema within.
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Example: `describe SomeClass, :migration, schema: 20170608152748`.
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## Available helpers
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Use `table` helper to create a temporary `ActiveRecord::Base` derived model
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for a table.
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Use `migrate!` helper to run the migration that is under test. It will not only
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run migration, but will also bump the schema version in the `schema_migrations`
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table. It is necessary because in the `after` hook we trigger the rest of
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the migrations, and we need to know where to start.
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See `spec/support/migrations_helpers.rb` for all the available helpers.
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## An example
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```ruby
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require 'spec_helper'
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# Load a migration class.
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require Rails.root.join('db', 'post_migrate', '20170526185842_migrate_pipeline_stages.rb')
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describe MigratePipelineStages, :migration do
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# Create test data - pipeline and CI/CD jobs.
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let(:jobs) { table(:ci_builds) }
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let(:stages) { table(:ci_stages) }
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let(:pipelines) { table(:ci_pipelines) }
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let(:projects) { table(:projects) }
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before do
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projects.create!(id: 123, name: 'gitlab1', path: 'gitlab1')
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pipelines.create!(id: 1, project_id: 123, ref: 'master', sha: 'adf43c3a')
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jobs.create!(id: 1, commit_id: 1, project_id: 123, stage_idx: 2, stage: 'build')
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jobs.create!(id: 2, commit_id: 1, project_id: 123, stage_idx: 1, stage: 'test')
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end
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# Test the migration.
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it 'correctly migrates pipeline stages' do
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expect(stages.count).to be_zero
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migrate!
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expect(stages.count).to eq 2
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expect(stages.all.pluck(:name)).to match_array %w[test build]
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end
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end
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```
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## Best practices
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1. Note that this type of tests do not run within the transaction, we use
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a truncation database cleanup strategy. Do not depend on transaction being
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present.
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