lib/src/frontend/expect.dart

// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:matcher/matcher.dart';

import '../backend/closed_exception.dart';
import '../backend/invoker.dart';

/// An exception thrown when a test assertion fails.
class TestFailure {
  final String message;

  TestFailure(this.message);

  String toString() => message;
}

/// The type used for functions that can be used to build up error reports
/// upon failures in [expect].
typedef String ErrorFormatter(
    actual, Matcher matcher, String reason, Map matchState, bool verbose);

/// Assert that [actual] matches [matcher].
///
/// This is the main assertion function. [reason] is optional and is typically
/// not supplied, as a reason is generated from [matcher]; if [reason]
/// is included it is appended to the reason generated by the matcher.
///
/// [matcher] can be a value in which case it will be wrapped in an
/// [equals] matcher.
///
/// If the assertion fails a [TestFailure] is thrown.
///
/// If [skip] is a String or `true`, the assertion is skipped. The arguments are
/// still evaluated, but [actual] is not verified to match [matcher]. If
/// [actual] is a [Future], the test won't complete until the future emits a
/// value.
///
/// If [skip] is a string, it should explain why the assertion is skipped; this
/// reason will be printed when running the test.
///
/// In some cases extra diagnostic info can be produced on failure (for
/// example, stack traces on mismatched exceptions). To enable these,
/// [verbose] should be specified as `true`.
void expect(actual, matcher,
    {String reason, skip, bool verbose: false, ErrorFormatter formatter}) {
  if (Invoker.current == null) {
    throw new StateError("expect() may only be called within a test.");
  }

  if (Invoker.current.closed) throw new ClosedException();

  if (skip != null && skip is! bool && skip is! String) {
    throw new ArgumentError.value(skip, "skip", "must be a bool or a String");
  }

  matcher = wrapMatcher(matcher);
  if (skip != null && skip != false) {
    String message;
    if (skip is String) {
      message = "Skip expect: $skip";
    } else if (reason != null) {
      message = "Skip expect ($reason).";
    } else {
      var description = new StringDescription().addDescriptionOf(matcher);
      message = "Skip expect ($description).";
    }

    Invoker.current.skip(message);
    return;
  }

  var matchState = {};
  try {
    if (matcher.matches(actual, matchState)) return;
  } catch (e, trace) {
    if (reason == null) {
      reason = '${(e is String) ? e : e.toString()} at $trace';
    }
  }
  if (formatter == null) formatter = _defaultFailFormatter;
  fail(formatter(actual, matcher, reason, matchState, verbose));
}

/// Convenience method for throwing a new [TestFailure] with the provided
/// [message].
void fail(String message) => throw new TestFailure(message);

// The default error formatter.
String _defaultFailFormatter(
    actual, Matcher matcher, String reason, Map matchState, bool verbose) {
  var description = new StringDescription();
  description.add('Expected: ').addDescriptionOf(matcher).add('\n');
  description.add('  Actual: ').addDescriptionOf(actual).add('\n');

  var mismatchDescription = new StringDescription();
  matcher.describeMismatch(actual, mismatchDescription, matchState, verbose);

  if (mismatchDescription.length > 0) {
    description.add('   Which: ${mismatchDescription}\n');
  }
  if (reason != null) description.add(reason).add('\n');
  return description.toString();
}