Added optional max limit override to errorIfWouldGoOverLimit

refs https://github.com/TryGhost/Team/issues/587

- The optional {max} passed as an option allows to override currently configured limit and do a theoretical new limit check. For example:  check if the max limit will be exceeded if the limit changes (user changes plans)

ghost/limit-service/lib/limit.js

@@ -81,12 +81,20 @@ class MaxLimit extends Limit {
         return await this.currentCountQueryFn(this.db);
     }
 
-    async errorIfWouldGoOverLimit() {
+    /**
+     * Throws a HostLimitError if the configured or passed max limit is ecceded by currentCountQuery
+     *
+     * @param {Object} options
+     * @param {Number} [options.max] - overrides configured default max value to perform checks against
+     */
+    async errorIfWouldGoOverLimit({max} = {}) {
         let currentCount = await this.currentCountQuery(this.db);
-        if ((currentCount + 1) > this.max) {
+
+        if ((currentCount + 1) > (max || this.max)) {
             throw this.generateError(currentCount);
         }
     }
+
     async errorIfIsOverLimit() {
         let currentCount = await this.currentCountQuery(this.db);
         if (currentCount > this.max) {

ghost/limit-service/test/limit.test.js

@@ -66,5 +66,34 @@ describe('Limit Service', function () {
 
             await limit.errorIfWouldGoOverLimit();
         });
+
+        it('ignores default configured max limit when it is passed explicitly', async function () {
+            const config = {
+                max: 10,
+                currentCountQuery: () => 10
+            };
+
+            const limit = new MaxLimit({name: 'maxy', config});
+
+            // should pass as the limit is overridden to 10 + 1 = 11
+            await limit.errorIfWouldGoOverLimit({max: 11});
+
+            try {
+                // should fail because limit is overridden to 10 + 1 < 1
+                await limit.errorIfWouldGoOverLimit({max: 1});
+                should.fail(limit, 'Should have errored');
+            } catch (err) {
+                should.exist(err);
+
+                should.exist(err.errorType);
+                should.equal(err.errorType, 'HostLimitError');
+
+                should.exist(err.errorDetails);
+                should.equal(err.errorDetails.name, 'maxy');
+
+                should.exist(err.message);
+                should.equal(err.message, 'This action would exceed the maxy limit on your current plan.');
+            }
+        });
     });
 });