Added automatic collection validation

refs https://github.com/TryGhost/Team/issues/3170

- When an automatic collection is created it should always have a valid filter assigned

ghost/collections/src/Collection.ts

@@ -5,7 +5,11 @@ import ObjectID from 'bson-objectid';
 
 const messages = {
     invalidIDProvided: 'Invalid ID provided for Collection',
-    invalidDateProvided: 'Invalid date provided for {fieldName}'
+    invalidDateProvided: 'Invalid date provided for {fieldName}',
+    invalidFilterProvided: {
+        message: 'Invalid filter provided for automatic Collection',
+        context: 'Automatic type of collection should always have a filter value'
+    }
 };
 
 export class Collection {
@@ -109,6 +113,13 @@ export class Collection {
             });
         }
 
+        if (data.type === 'automatic' && !data.filter) {
+            throw new ValidationError({
+                message: tpl(messages.invalidFilterProvided.message),
+                context: tpl(messages.invalidFilterProvided.context)
+            });
+        }
+
         return new Collection({
             id: id.toHexString(),
             title: data.title,

ghost/collections/test/Collection.test.ts

@@ -88,7 +88,7 @@ describe('Collection', function () {
     });
 
     it('Throws an error when trying to create a Collection with an invalid ID', async function () {
-        assert.rejects(async () => {
+        await assert.rejects(async () => {
             await Collection.create({
                 id: 12345
             });
@@ -99,7 +99,7 @@ describe('Collection', function () {
     });
 
     it('Throws an error when trying to create a Collection with invalid created_at date', async function () {
-        assert.rejects(async () => {
+        await assert.rejects(async () => {
             await Collection.create({
                 created_at: 'invalid date'
             });
@@ -109,6 +109,19 @@ describe('Collection', function () {
         });
     });
 
+    it('Throws an error when trying to create an automatic Collection without a filter', async function () {
+        await assert.rejects(async () => {
+            await Collection.create({
+                type: 'automatic',
+                filter: null
+            });
+        }, (err: any) => {
+            assert.equal(err.message, 'Invalid filter provided for automatic Collection', 'Error message should match');
+            assert.equal(err.context, 'Automatic type of collection should always have a filter value', 'Error message should match');
+            return true;
+        });
+    });
+
     it('Can add posts to different positions', async function () {
         const collection = await Collection.create({
             title: 'Testing adding posts'