Added test coverage for max limit class

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

- Test were missing for class initialization and around how the limit currently works.
- Before extending it's behavior throught its valuable to cover current functionality to not accidentally break anything

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

@@ -0,0 +1,57 @@
+// Switch these lines once there are useful utils
+// const testUtils = require('./utils');
+require('./utils');
+
+const {MaxLimit} = require('../lib/limit');
+
+describe('Limit Service', function () {
+    describe('Max Limit', function () {
+        it('throws if initialized without a current count query', function () {
+            const config = {};
+
+            try {
+                const limit = new MaxLimit({name: 'no accountability!', config});
+                should.fail(limit, 'Should have errored');
+            } catch (err) {
+                should.exist(err);
+                should.exist(err.errorType);
+                should.equal(err.errorType, 'IncorrectUsageError');
+            }
+        });
+
+        it('throws if would go over the limit', async function () {
+            const config = {
+                max: 1,
+                currentCountQuery: () => 1
+            };
+            const limit = new MaxLimit({name: 'maxy', config});
+
+            try {
+                await limit.errorIfWouldGoOverLimit();
+                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.');
+            }
+        });
+
+        it('passes if does not go over the limit', async function () {
+            const config = {
+                max: 2,
+                currentCountQuery: () => 1
+            };
+
+            const limit = new MaxLimit({name: 'maxy', config});
+
+            await limit.errorIfWouldGoOverLimit();
+        });
+    });
+});