unexpected/lib/createStandardErrorMessage.js

const AssertionString = require('./AssertionString');

module.exports = function createStandardErrorMessage(
  output,
  subject,
  testDescription,
  args,
  options = {}
) {
  const preamble = 'expected';

  const subjectOutput = output.clone();
  if (subject) {
    subject.call(subjectOutput, subjectOutput);
  }

  const argsOutput = output.clone();
  if (typeof args === 'function') {
    args.call(argsOutput, argsOutput);
  } else {
    if (args.length > 0) {
      let previousWasAssertion = false;
      args.forEach((arg, index) => {
        const isAssertion =
          arg && typeof arg === 'object' && arg instanceof AssertionString;
        if (index > 0) {
          if (!isAssertion && !previousWasAssertion) {
            argsOutput.text(',');
          }
          argsOutput.sp();
        }
        if (isAssertion) {
          argsOutput.error(arg.text);
        } else {
          arg.call(argsOutput, argsOutput);
        }
        previousWasAssertion = isAssertion;
      });
    }
  }

  const subjectSize = subjectOutput.size();
  const argsSize = argsOutput.size();
  const width =
    preamble.length +
    subjectSize.width +
    argsSize.width +
    testDescription.length;
  const height = Math.max(subjectSize.height, argsSize.height);

  if ('omitSubject' in output && output.omitSubject === options.subject) {
    const matchTestDescription = /^(not )?to (.*)/.exec(testDescription);
    if (matchTestDescription) {
      output.error('should ');
      if (matchTestDescription[1]) {
        output.error('not ');
      }
      testDescription = matchTestDescription[2];
    } else {
      testDescription = `expected: ${testDescription}`;
    }
  } else if (
    options.compact &&
    options.compactSubject &&
    (subjectSize.height > 1 || subjectSize.width > (options.compactWidth || 35))
  ) {
    output.error('expected').sp();
    options.compactSubject.call(output, output);
    output.sp();
  } else {
    output.error(preamble);
    if (subjectSize.height > 1) {
      output.nl();
    } else {
      output.sp();
    }
    output.append(subjectOutput);
    if (
      subjectSize.height > 1 ||
      (height === 1 && width > output.preferredWidth)
    ) {
      output.nl();
    } else {
      output.sp();
    }
  }

  output.error(testDescription);

  if (argsSize.height > 1) {
    output.nl();
  } else if (argsSize.width > 0) {
    output.sp();
  }

  output.append(argsOutput);

  return output;
};