ParserStateTests.fs

namespace PidginFsharp.Test

open PidginFsharp
open System
open Xunit

module ParserStateTests =
    [<Fact>]
    let ``peek returns the first character`` () =
        let actual = ParserState.createStringParserState "abc" |> ParserState.peek
        let expected = Some 'a'
        Assert.Equal<char option>(expected, actual)

    [<Fact>]
    let ``advance moves one character further`` () =
        let state = ParserState.createStringParserState "abc"
        state |> ParserState.advance
        let actual = state |> ParserState.peek
        let expected = Some 'b'
        Assert.Equal<char option>(expected, actual)

    [<Fact>]
    let ``after advancing after the end peek returns None`` () =
        let state = ParserState.createStringParserState "abc"
        state |> ParserState.advance
        state |> ParserState.advance
        state |> ParserState.advance

        let actual = ParserState.peek state
        let expected = None
        Assert.Equal<char option>(expected, actual)