Add tests to verify db version hasn't changed

issue TryGhost#4479

- these tests will need updating if ever the db schema (not inc validations), permissions fixtures or db
version ever changes
- the intention is that it is no longer possible to accidentally change permissions or the db schema without
knowing you need to update the db version and the values in this test file

core/test/unit/migration_spec.js

@@ -0,0 +1,48 @@
+/*globals describe, it*/
+/*jshint expr:true*/
+var should          = require('should'),
+    _               = require('lodash'),
+    crypto          = require('crypto'),
+
+    // Stuff we are testing
+    defaultSettings = require('../../server/data/default-settings'),
+    schema          = require('../../server/data/schema'),
+    permissions     = require('../../server/data/fixtures/permissions/permissions');
+
+// To stop jshint complaining
+should.equal(true, true);
+
+describe('Migrations', function () {
+    // These tests exist to ensure that developers are not able to modify the database schema, or permissions fixtures
+    // without knowing that they also need to update the default database version,
+    // both of which are required for migrations to work properly.
+
+    describe('DB version integrity', function () {
+        // Only these variables should need updating
+        var currentDbVersion = '003',
+            currentSchemaHash = '4f2a9e139f4c3dcf04e3006ea8ebba97',
+            currentPermissionsHash = '42e486732270cda623fc5efc04808c0c';
+
+        // If this test is failing, then it is likely a change has been made that requires a DB version bump,
+        // and the values above will need updating as confirmation
+        it('should not change without fixing this test', function () {
+            var tablesNoValidation = _.cloneDeep(schema.tables),
+                schemaHash,
+                permissionsHash;
+
+            _.each(tablesNoValidation, function (table) {
+                return _.each(table, function (column, name) {
+                    table[name] = _.omit(column, 'validations');
+                });
+            });
+
+            schemaHash = crypto.createHash('md5').update(JSON.stringify(tablesNoValidation)).digest('hex');
+            permissionsHash = crypto.createHash('md5').update(JSON.stringify(permissions)).digest('hex');
+
+            // Test!
+            defaultSettings.core.databaseVersion.defaultValue.should.eql(currentDbVersion);
+            schemaHash.should.eql(currentSchemaHash);
+            permissionsHash.should.eql(currentPermissionsHash);
+        });
+    });
+});