there needs to be another test with
parseBinding('a( b() | c )')

There is no need to test this because it works, trust me :)

In in ideal world, there should be a test for any kind of primary expression. But visiting the tree to check the expression is really a pain and I don't want to go this road.

Once we have a visitor to convert an AST back to an exp, we can add more test, ie
expect(toExpression(parseBinding('a( b() | c )').ast)).toEqual('a(b()|c').

There is an issue for that #1949 - it would be great if someone from the community could tackle this.

it's not that I don't trust you. I'm only suggesting the error wasn't with that example because that already worked alpha.21. The problem is when you introduce more parentheses inside of the arguments with a pipe. In the jsbint above if you change
{{ wat(number.get | async) }} to {{ wat(number.getAsync() | async) }} then you will see the error

I know what you mean and it was because AccessMember and MethodCall were not handled in the same way, see https://github.com/angular/angular/pull/2348/files#diff-a200f3d86e80e2bea53a7a9ca4d40a10L475 above, Pipe were parsed only for the former and not for the later.

As explained above, parse are now parsed for any Primary expression (https://github.com/angular/angular/pull/2348/files#diff-a200f3d86e80e2bea53a7a9ca4d40a10R424) and to be exhaustive we would need to test all the 10 cases. I prefer to defer that to when we can convert AST back to expressions.

Note that referring to the issue from my previous comment has added a link there and we should add those tests when we'll add the visitor.

I understand now, thanks for clearing that up for me 👍

Still you're probably right about adding a test for a(b.c|d) as c is not a PE. We really need to come with ast -> exp before merging this and add more tests.