add tests for .. associativity

Author: tyru

test/test1.ok

@@ -59,6 +59,8 @@
 (let %= a 5)
 (let ..= a 'foo')
 (echo (concat (concat 'foo' 'bar') 'baz'))
+(echo (concat 'foo' (concat 'bar' 'baz')))
+(echo (concat (concat 'foo' 'bar') 'baz'))
 (let = a '🐥')
 (const = a 1)
 (const = (a b) (list 1 2))

test/test1.vim

@@ -66,6 +66,8 @@ let a /= 4
 let a %= 5
 let a ..= 'foo'
 echo ('foo' .. 'bar')..'baz'
+echo 'foo' .. ('bar'..'baz')
+echo 'foo' .. 'bar' .. 'baz'
 let a = '🐥'
 const a = 1
 const [a, b] = [1, 2]