Drop `position` column from `security_findings` table

- Drop column
- Add specs

Changelog: removed
MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/78665

db/post_migrate/20220120094340_drop_position_from_security_findings.rb

+# frozen_string_literal: true
+
+class DropPositionFromSecurityFindings < Gitlab::Database::Migration[1.0]
+  enable_lock_retries!
+
+  def change
+    remove_column :security_findings, :position, :integer
+  end
+end

db/schema_migrations/20220120094340

+69d8283501ba6a4946a60e3812fe2cf3031fc4a915d6e7c6fac3bf272423f2f2
\ No newline at end of file

db/structure.sql

@@ -19394,7 +19394,6 @@ CREATE TABLE security_findings (
     confidence smallint NOT NULL,
     project_fingerprint text,
     deduplicated boolean DEFAULT false NOT NULL,
-    "position" integer,
     uuid uuid,
     overridden_uuid uuid,
     CONSTRAINT check_b9508c6df8 CHECK ((char_length(project_fingerprint) <= 40))
@@ -27553,8 +27552,6 @@ CREATE INDEX index_security_findings_on_project_fingerprint ON security_findings
 
 CREATE INDEX index_security_findings_on_scan_id_and_deduplicated ON security_findings USING btree (scan_id, deduplicated);
 
-CREATE UNIQUE INDEX index_security_findings_on_scan_id_and_position ON security_findings USING btree (scan_id, "position");
-
 CREATE INDEX index_security_findings_on_scanner_id ON security_findings USING btree (scanner_id);
 
 CREATE INDEX index_security_findings_on_severity ON security_findings USING btree (severity);

spec/migrations/20220120094340_drop_position_from_security_findings_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require_migration!('drop_position_from_security_findings')
+
+RSpec.describe DropPositionFromSecurityFindings do
+  let(:events) { table(:security_findings) }
+
+  it 'correctly migrates up and down' do
+    reversible_migration do |migration|
+      migration.before -> {
+        expect(events.column_names).to include('position')
+      }
+
+      migration.after -> {
+        events.reset_column_information
+        expect(events.column_names).not_to include('position')
+      }
+    end
+  end
+end