Add cop for use of remove_columnadd-remove-column-cop

remove_column should only be used in the up (or change) step of a migration if
it's a post-deployment migration. Otherwise there will be downtime due to the
ActiveRecord column cache, which we can avoid by using the IgnorableColumn
concern in combination with a post-deployment migration.

1 files changed, 68 insertions, 0 deletions

diff --git a/spec/rubocop/cop/migration/remove_column_spec.rb b/spec/rubocop/cop/migration/remove_column_spec.rb
new file mode 100644
index 00000000000..89112f01723
--- /dev/null
+++ b/spec/rubocop/cop/migration/remove_column_spec.rb
@@ -0,0 +1,68 @@
+require 'spec_helper'
+
+require 'rubocop'
+require 'rubocop/rspec/support'
+
+require_relative '../../../../rubocop/cop/migration/remove_column'
+
+describe RuboCop::Cop::Migration::RemoveColumn do
+  include CopHelper
+
+  subject(:cop) { described_class.new }
+
+  def source(meth = 'change')
+    "def #{meth}; remove_column :table, :column; end"
+  end
+
+  context 'in a regular migration' do
+    before do
+      allow(cop).to receive(:in_migration?).and_return(true)
+      allow(cop).to receive(:in_post_deployment_migration?).and_return(false)
+    end
+
+    it 'registers an offense when remove_column is used in the change method' do
+      inspect_source(cop, source('change'))
+
+      aggregate_failures do
+        expect(cop.offenses.size).to eq(1)
+        expect(cop.offenses.map(&:line)).to eq([1])
+      end
+    end
+
+    it 'registers an offense when remove_column is used in the up method' do
+      inspect_source(cop, source('up'))
+
+      aggregate_failures do
+        expect(cop.offenses.size).to eq(1)
+        expect(cop.offenses.map(&:line)).to eq([1])
+      end
+    end
+
+    it 'registers no offense when remove_column is used in the down method' do
+      inspect_source(cop, source('down'))
+
+      expect(cop.offenses.size).to eq(0)
+    end
+  end
+
+  context 'in a post-deployment migration' do
+    before do
+      allow(cop).to receive(:in_migration?).and_return(true)
+      allow(cop).to receive(:in_post_deployment_migration?).and_return(true)
+    end
+
+    it 'registers no offense' do
+      inspect_source(cop, source)
+
+      expect(cop.offenses.size).to eq(0)
+    end
+  end
+
+  context 'outside of a migration' do
+    it 'registers no offense' do
+      inspect_source(cop, source)
+
+      expect(cop.offenses.size).to eq(0)
+    end
+  end
+end