const tests = [
  ' ',
  '  ',
  'aa',
  'aa ',
  ' aa',
  'a b',
  'aa bb',
  'aa  bb',
  'aa   bb',
  'aa    bb',
  'aa   bb   cc',
  '  aa   bb   cc  ',
  '   aa   bb   cc   ',
];

function runTests() {
  for (test of tests) {
    const expected = test.replace(/ +/g, ' ');
    const real = replaceSpace(test);
    if (expected !== real) {
      console.log(`
      test: -${test}-
      expected: -${expected}-
      result: -${real}-
      `);
    }
  }
}