ANTLR4 Visitor testing

Question

I have described the grammar, it works fine. Now I'm at the point where I need to write unit tests for it. Does anyone know how to do this properly? I am using Java.
And how can I test the visitor with small programs that he will visit? Suppose I want to put some files in the resource directory, read the source code of the program from there and get the results for testing.

Could you give me a small example of how I can test this. For example, I have this method:

    @Override
    public Atom visitInt(final ProgramParser.IntContext ctx) {
        return new Value(Integer.parseInt(ctx.INT().getText()));
    }

Answer 1

Let's say your grammar looks like this:

grammar Program;

parse
 : int EOF
 ;

int
 : Int
 ;

Int
 : [0-9]+
 ;

And your visitor like this:

public class DemoVisitor extends ProgramBaseVisitor<Atom> {

    @Override
    public Atom visitInt(ProgramParser.IntContext ctx) {
        return new Atom(ctx.Int().getText());
    }
}

class Atom {

    public final String value;

    public Atom(String value) {
        this.value = value;
    }
}

then this can be tested like:

@Test
public void visitorTest() {

    ProgramLexer lexer = new ProgramLexer(CharStreams.fromString("42"));
    ProgramParser parser = new ProgramParser(new CommonTokenStream(lexer));

    Atom atom = new DemoVisitor().visit(parser.int_());

    Assert.assertEquals("42", atom.value);
}