Add tests for string indexing and converting lists to strings

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

tests/str.npp

@@ -40,6 +40,17 @@ println(a * 4)
 println(b * 5)
 println((a * 6).to_repr())
 
+# __index__
+println("__index__")
+println(a[0])
+println(a[1])
+println(a[2])
+println(a[3])
+println(a[-1])
+println(a[-2])
+println(a[-3])
+println(a[-4])
+
 # constructor
 println("constructor")
 println(Str("asdf"))
@@ -47,3 +58,5 @@ println(Str(1234))
 println(Str(1.0))
 println(Str(true))
 println(Str(false))
+println(Str([1, 2, 3]))
+println(Str([]))

tests/str.npp.expect

@@ -24,9 +24,20 @@ __mul__
 asdfasdfasdfasdf
 This is a longer sentenceThis is a longer sentenceThis is a longer sentenceThis is a longer sentenceThis is a longer sentence
 'asdfasdfasdfasdfasdfasdf'
+__index__
+a
+s
+d
+f
+f
+d
+s
+a
 constructor
 asdf
 1234
 1.0
 true
 false
+[1, 2, 3]
+[]