test: Add tests for push (#614)

* Add support for the Jekyll sample filter

See https://jekyllrb.com/docs/liquid/filters

I am sorting the array randomly and then picking the first N items or all items if there is no sample limit.

* Add tests for `push`

I thought `push` was broken because it doesn't work on the Playground but that's not the case. Here are the tests to prove it. Taken from the `concat` tests.

* Remove the sample experiment

This got in from another branch lol.

* Recommend the build:dist command over the whole build

This one works for me locally whereas build:docs is reporting some issues.

* Return the full `build` command and explain how to use `commitlint` to workshop the message

I am working on a PR to make `build` run on macOS because it is a part of the pre-commit hook anyway so all contributors should make it work for them.

I have also shown how to check your messages against `commitlint` from the CLI because it is faster than using the VS Code GUI.

test/integration/filters/array.spec.ts

@@ -92,6 +92,27 @@ describe('filters/array', function () {
     })
   })
 
+  describe('push', () => {
+    it('should push arg value', async () => {
+      const scope = { val: ['hey'], arg: 'foo' }
+      await test('{{ val | push: arg | join: "," }}', scope, 'hey,foo')
+    })
+    it('should support undefined left value', async () => {
+      const scope = { arg: 'foo' }
+      await test('{{ notDefined | push: arg | join: "," }}', scope, 'foo')
+    })
+    it('should ignore nil left value', async () => {
+      const scope = { undefinedValue: undefined, nullValue: null, arg: 'foo' }
+      await test('{{ undefinedValue | push: arg | join: "," }}', scope, 'foo')
+      await test('{{ nullValue | push: arg | join: "," }}', scope, 'foo')
+    })
+    it('should ignore nil right value', async () => {
+      const scope = { nullValue: null }
+      await test('{{ nullValue | push | join: "," }}', scope, '')
+      await test('{{ nullValue | push: nil | join: "," }}', scope, '')
+    })
+  })
+
   describe('reverse', function () {
     it('should support reverse', () => test(
       '{{ "Ground control to Major Tom." | split: "" | reverse | join: "" }}',