gramjs/__tests__/extensions/Scanner.spec.js

const Scanner = require("../../gramjs/extensions/Scanner");

const helloScanner = new Scanner("Hello world");

describe("Scanner", () => {
  beforeEach(() => helloScanner.reset());

  test("it should construct a new Scanner", () => {
    expect(helloScanner.str).toEqual("Hello world");
    expect(helloScanner.pos).toEqual(0);
    expect(helloScanner.lastMatch).toBeNull();
  });

  describe(".chr", () => {
    test("it should return the character at the current pos", () => {
      expect(helloScanner.chr).toEqual("H");
    });
  });

  describe(".peek", () => {
    test("it should return the character at the current pos", () => {
      expect(helloScanner.peek()).toEqual("H");
    });

    test("it should return the next n characters", () => {
      expect(helloScanner.peek(3)).toEqual("Hel");
      expect(helloScanner.peek(5)).toEqual("Hello");
    });
  });

  describe(".consume", () => {
    test("it should consume the current character", () => {
      const char = helloScanner.consume();
      expect(char).toEqual("H");
      expect(helloScanner.pos).toEqual(1);
    });

    test("it should consume the next n characters", () => {
      const chars = helloScanner.consume(5);
      expect(chars).toEqual("Hello");
      expect(helloScanner.pos).toEqual(5);
    });
  });

  describe(".reverse", () => {
    test("it should set pos back n characters", () => {
      helloScanner.consume(5);
      helloScanner.reverse(5);
      expect(helloScanner.pos).toEqual(0);
    });

    test("it should not go back further than 0", () => {
      helloScanner.reverse(10);
      expect(helloScanner.pos).toEqual(0);
    });
  });

  describe(".scanUntil", () => {
    test("it should scan the string for a regular expression starting at the current pos", () => {
      helloScanner.scanUntil(/w/);
      expect(helloScanner.pos).toEqual(6);
    });

    test("it should do nothing if the pattern is not found", () => {
      helloScanner.scanUntil(/G/);
      expect(helloScanner.pos).toEqual(0);
    });
  });

  describe(".rest", () => {
    test("it should return the unconsumed input", () => {
      helloScanner.consume(6);
      expect(helloScanner.rest).toEqual("world");
    });
  });

  describe(".reset", () => {
    test("it should reset the pos to 0", () => {
      helloScanner.consume(5);
      helloScanner.reset();
      expect(helloScanner.pos).toEqual(0);
    });
  });

  describe(".eof", () => {
    test("it should return true if the scanner has reached the end of the input", () => {
      expect(helloScanner.eof()).toBe(false);
      helloScanner.consume(11);
      expect(helloScanner.eof()).toBe(true);
    });
  });

  describe(".bof", () => {
    test("it should return true if pos is 0", () => {
      expect(helloScanner.bof()).toBe(true);
      helloScanner.consume(11);
      expect(helloScanner.bof()).toBe(false);
    });
  });
});