more tests on interpolate string

more tests on interpolate string:
    describe "parse interpolate string: ",  ->
      it "parse a", ->
        expect(str parse('"a"')).to.equal '[string! "a"]'
      it "parse $a", ->
        expect(str parse('"$a"')).to.equal "[string! a]"
      it "parse $a:", ->
        expect(str parse('"$a:"')).to.equal "[string! a: a]"
      it "parse $a\\:", ->
        expect(str parse('"$a\\:"')).to.equal "[string! a \"\\:\"]"
      it "parse $", ->
        expect(str parse('"$"')).to.equal "[string! \"$\"]"
      it "parse a\\b", ->
        expect(str parse('"a\\b"')).to.equal '[string! "a\\b"]'
      it "parse '''a\"'\\n'''", ->
        expect(str parse('"""a\\"\'\\n"""')).to.equal "[string! \"a\\\\\"'\\\\n\"]"