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.

CONTRIBUTING.md

@@ -0,0 +1,31 @@
+# Contributing
+
+1. Build everything and run tests to learn how to do both:
+  - `npm run build`
+  - `npm run test`
+
+  Tests won't at first unless you've done a build at least once.
+  Subsequent changes to tests do not need re-builds but changes to the code and
+  then tests need a build to pick up the new code by the tests.
+
+2. Make your changes and add a test for them
+  - Build after you've made your changes
+  - Run tests as per the above to validate your changes
+
+3. Create a pull request
+  - Ensure the build runs because the Husky pre-commit hook checks it
+    - `npm run check` checks runs the build, tests, lint and perf tests
+    - `commitlint` checks the commit message format
+    
+    If there is a problem you will see it in the pre-commit hook output.
+    In VS Code, this output will be shown in a new file in a new tab if the
+    pre-commit hook fails.
+    If you want to check the commit message without using the VS Code Source
+    Control UI, you can run `echo "feat: my commit message" > npx commitlint`
+    directly.
+    
+  - `git switch -c your_branch_name` (do this in your fork not the main repo)
+  - `git add .`
+  - `git commit -m "feat: Adding my change"`
+  - `git push`
+  - Go to GitHub and find your fork, open a PR against the upstream from it

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: "" }}',