Double Output

Print the input twice, without anything in between, no matter how it looks.

Judge

(async function*(context: Context): Challenge {
    const check = (input: string) => (stdout: string): TestCase => {
        const expected = input + input;
        const pass = stdout === expected || stdout === expected + '\n' || stdout === expected + '\r\n'; // multiple trailing newlines or other whitespace are not allowed
        return new TestCase(undefined, pass ? "Pass" : "Fail", { Diff: { expected: expected.at(-1) === '\n' ? expected + '\n' : expected, output: stdout } });
    }
    const testCases = [['one line', 'abcdefg'], ['multiple lines', 'a\nbc'], ['trailing newline', 'abc\n'], ['no input', '']];
    for (const [name, input] of testCases) {
        yield (await context.run(input)).assert(check(input)).setName(name)
    }
    return context.noFailures();
})

Example Code

const fs = require('fs');

const input = fs.readFileSync(0, 'utf-8');

console.log(input + input);