Improved error messages from unittest.

pkg/unittest/test/matchers_test.dart

 // Copyright (c) 2012, 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 'dart:async';
 import 'dart:collection';
 
 import 'package:unittest/unittest.dart';
 
 import 'test_common.dart';
 import 'test_utils.dart';
 
 void main() {
 
   initUtils();
 
   // Core matchers
 
   group('Core matchers', () {
 
     test('isTrue', () {
       shouldPass(true, isTrue);
-      shouldFail(false, isTrue, "Expected: true But: was <false>. "
-          "Actual: <false>");
+      shouldFail(false, isTrue, "Expected: true Actual: <false>");
     });
 
     test('isFalse', () {
       shouldPass(false, isFalse);
-      shouldFail(10, isFalse, "Expected: false But: was <10>. "
-          "Actual: <10>");
-      shouldFail(true, isFalse, "Expected: false But: was <true>. "
-          "Actual: <true>");
+      shouldFail(10, isFalse, "Expected: false Actual: <10>");
+      shouldFail(true, isFalse, "Expected: false Actual: <true>");
     });
 
     test('isNull', () {
       shouldPass(null, isNull);
-      shouldFail(false, isNull, "Expected: null But: was <false>. "
-          "Actual: <false>");
+      shouldFail(false, isNull, "Expected: null Actual: <false>");
     });
 
     test('isNotNull', () {
       shouldPass(false, isNotNull);
-      shouldFail(null, isNotNull, "Expected: not null But: was <null>. "
-          "Actual: <null>");
+      shouldFail(null, isNotNull, "Expected: not null Actual: <null>");
     });
 
     test('same', () {
       var a = new Map();
       var b = new Map();
       shouldPass(a, same(a));
-      shouldFail(b, same(a), "Expected: same instance as {} But: was {}. "
-          "Actual: {}");
+      shouldFail(b, same(a), "Expected: same instance as {} Actual: {}");
     });
 
     test('equals', () {
       var a = new Map();
       var b = new Map();
       shouldPass(a, equals(a));
       shouldPass(a, equals(b));
     });
 
     test('anything', () {
       var a = new Map();
       shouldPass(0, anything);
       shouldPass(null, anything);
       shouldPass(a, anything);
-      shouldFail(a, isNot(anything), "Expected: not anything "
-          "But: was {}. Actual: {}");
+      shouldFail(a, isNot(anything), "Expected: not anything Actual: {}");
     });
 
     test('throws', () {
       shouldFail(doesNotThrow, throws,
           matches(
-              r"Expected: throws an exception +But:  no exception\."
-              r"Actual: <Closure(: \(dynamic\) => dynamic "
-                  r"from Function 'doesNotThrow': static\.)?>"));
+              r"Expected: throws"
+              r"  Actual: <Closure(: \(dynamic\) => dynamic "
+              r"from Function 'doesNotThrow': static\.)?>"
+              r"   Which: did not throw"));
       shouldPass(doesThrow, throws);
       shouldFail(true, throws,
-          "Expected: throws an exception But: not a Function or Future. "
-          "Actual: <true>");
+          "Expected: throws"
+          "  Actual: <true>"
+          "   Which: is not a Function or Future");
     });
 
     test('throwsA', () {
       shouldPass(doesThrow, throwsA(equals('X')));
       shouldFail(doesThrow, throwsA(equals('Y')),
           matches(
-              r"Expected: throws an exception which matches 'Y' +"
-              r"But:  exception 'X' does not match 'Y'\."
-              r"Actual: <Closure(: \(dynamic\) => dynamic "
-                  r"from Function 'doesThrow': static\.)?>"));
+              r"Expected: throws 'Y'"
+              r"  Actual: <Closure(: \(dynamic\) => dynamic "
+              r"from Function 'doesThrow': static\.)?>"
+              r"   Which: threw 'X'"));
     });
 
     test('returnsNormally', () {
       shouldPass(doesNotThrow, returnsNormally);
       shouldFail(doesThrow, returnsNormally,
           matches(
-              r"Expected: return normally +But:  threw 'X'\."
-              r"Actual: <Closure(: \(dynamic\) => dynamic "
-                  r"from Function 'doesThrow': static\.)?>"));
+              r"Expected: return normally"
+              r"  Actual: <Closure(: \(dynamic\) => dynamic "
+              r"from Function 'doesThrow': static\.)?>"
+              r"   Which: threw 'X'"));
     });
 
+
     test('hasLength', () {
       var a = new Map();
       var b = new List();
       shouldPass(a, hasLength(0));
       shouldPass(b, hasLength(0));
       shouldPass('a', hasLength(1));
       shouldFail(0, hasLength(0), new PrefixMatcher(
           "Expected: an object with length of <0> "
-          "But: had no length property."
-          "Actual: <0>"));
+          "Actual: <0> "
+          "Which: has no length property"));
 
       b.add(0);
       shouldPass(b, hasLength(1));
       shouldFail(b, hasLength(2),
           "Expected: an object with length of <2> "
-          "But: had length of <1>. "
-          "Actual: [0]");
+          "Actual: [0] "
+          "Which: has length of <1>");
 
       b.add(0);
       shouldFail(b, hasLength(1),
           "Expected: an object with length of <1> "
-          "But: had length of <2>. "
-          "Actual: [0, 0]");
+          "Actual: [0, 0] "
+          "Which: has length of <2>");
       shouldPass(b, hasLength(2));
     });
 
     test('scalar type mismatch', () {
       shouldFail('error', equals(5.1),
           "Expected: <5.1> "
-          "But: was 'error'. Actual: 'error'");
+          "Actual: 'error'");
     });
 
     test('nested type mismatch', () {
       shouldFail(['error'], equals([5.1]),
           "Expected: [5.1] "
-          "But: expected <5.1> but was 'error' mismatch at position 0. "
-          "Actual: ['error']");
+          "Actual: ['error'] "
+          "Which: has mismatch at position 0: expected <5.1> but is 'error'");
     });
 
+    // TODO(gram): we used to compound mismatch positions in nested arrays;
+    // try get that to work again.
     test('doubly-nested type mismatch', () {
       shouldFail([['error']], equals([[5.1]]),
           "Expected: [[5.1]] "
-          "But: expected <5.1> but was 'error' "
-          "mismatch at position 0 mismatch at position 0. "
-          "Actual: [['error']]");
+          "Actual: [['error']] "
+          "Which: has mismatch at position 0: "
+          "expected <5.1> but is 'error'");
     });
   });
 
   group('Numeric Matchers', () {
 
     test('greaterThan', () {
       shouldPass(10, greaterThan(9));
       shouldFail(9, greaterThan(10),
-        "Expected: a value greater than <10> But: was <9>. Actual: <9>");
+        "Expected: a value greater than <10> "
+        "Actual: <9> "
+        "Which: is not a value greater than <10>");
     });
 
     test('greaterThanOrEqualTo', () {
       shouldPass(10, greaterThanOrEqualTo(10));
       shouldFail(9, greaterThanOrEqualTo(10),
-        "Expected: a value greater than or equal to <10> But: was <9>. "
-        "Actual: <9>");
+        "Expected: a value greater than or equal to <10> "
+        "Actual: <9> "
+        "Which: is not a value greater than or equal to <10>");
     });
 
     test('lessThan', () {
-      shouldFail(10, lessThan(9), "Expected: a value less than <9> "
-          "But: was <10>. Actual: <10>");
+      shouldFail(10, lessThan(9),
+          "Expected: a value less than <9> "
+          "Actual: <10> "
+          "Which: is not a value less than <9>");
       shouldPass(9, lessThan(10));
     });
 
     test('lessThanOrEqualTo', () {
       shouldPass(10, lessThanOrEqualTo(10));
       shouldFail(11, lessThanOrEqualTo(10),
-        "Expected: a value less than or equal to <10> But: was <11>. "
-        "Actual: <11>");
+        "Expected: a value less than or equal to <10> "
+        "Actual: <11> "
+        "Which: is not a value less than or equal to <10>");
     });
 
     test('isZero', () {
       shouldPass(0, isZero);
-      shouldFail(1, isZero, "Expected: a value equal to <0> But: was <1>."
-          " Actual: <1>");
+      shouldFail(1, isZero, 
+          "Expected: a value equal to <0> "
+          "Actual: <1> "
+          "Which: is not a value equal to <0>");
     });
 
     test('isNonZero', () {
-      shouldFail(0, isNonZero, "Expected: a value not equal to <0> "
-          "But: was <0>. Actual: <0>");
+      shouldFail(0, isNonZero,
+          "Expected: a value not equal to <0> "
+          "Actual: <0> "
+          "Which: is not a value not equal to <0>");
       shouldPass(1, isNonZero);
     });
 
     test('isPositive', () {
-      shouldFail(-1, isPositive, "Expected: a positive value "
-          "But: was <-1>. Actual: <-1>");
-      shouldFail(0, isPositive, "Expected: a positive value "
-          "But: was <0>. Actual: <0>");
+      shouldFail(-1, isPositive,
+          "Expected: a positive value "
+          "Actual: <-1> "
+          "Which: is not a positive value");
+      shouldFail(0, isPositive, 
+          "Expected: a positive value "
+          "Actual: <0> "
+          "Which: is not a positive value");
       shouldPass(1, isPositive);
     });
 
     test('isNegative', () {
       shouldPass(-1, isNegative);
       shouldFail(0, isNegative,
-          "Expected: a negative value But: was <0>. Actual: <0>");
+          "Expected: a negative value "
+          "Actual: <0> "
+          "Which: is not a negative value");
     });
 
     test('isNonPositive', () {
       shouldPass(-1, isNonPositive);
       shouldPass(0, isNonPositive);
       shouldFail(1, isNonPositive,
-          "Expected: a non-positive value But: was <1>. Actual: <1>");
+          "Expected: a non-positive value "
+          "Actual: <1> "
+          "Which: is not a non-positive value");
     });
 
     test('isNonNegative', () {
       shouldPass(1, isNonNegative);
       shouldPass(0, isNonNegative);
       shouldFail(-1, isNonNegative,
-        "Expected: a non-negative value But: was <-1>. Actual: <-1>");
+        "Expected: a non-negative value "
+        "Actual: <-1> "
+        "Which: is not a non-negative value");
     });
 
     test('closeTo', () {
       shouldPass(0, closeTo(0, 1));
       shouldPass(-1, closeTo(0, 1));
       shouldPass(1, closeTo(0, 1));
       shouldFail(1.001, closeTo(0, 1),
           "Expected: a numeric value within <1> of <0> "
-          "But: differed by <1.001>. "
-          "Actual: <1.001>");
+          "Actual: <1.001> "
+          "Which: differs by <1.001>");
       shouldFail(-1.001, closeTo(0, 1),
           "Expected: a numeric value within <1> of <0> "
-          "But: differed by <1.001>. "
-          "Actual: <-1.001>");
+          "Actual: <-1.001> "
+          "Which: differs by <1.001>");
     });
 
     test('inInclusiveRange', () {
       shouldFail(-1, inInclusiveRange(0,2),
           "Expected: be in range from 0 (inclusive) to 2 (inclusive) "
-          "But: was <-1>. Actual: <-1>");
+          "Actual: <-1>");
       shouldPass(0, inInclusiveRange(0,2));
       shouldPass(1, inInclusiveRange(0,2));
       shouldPass(2, inInclusiveRange(0,2));
       shouldFail(3, inInclusiveRange(0,2),
           "Expected: be in range from 0 (inclusive) to 2 (inclusive) "
-          "But: was <3>. Actual: <3>");
+          "Actual: <3>");
     });
 
     test('inExclusiveRange', () {
       shouldFail(0, inExclusiveRange(0,2),
           "Expected: be in range from 0 (exclusive) to 2 (exclusive) "
-          "But: was <0>. Actual: <0>");
+          "Actual: <0>");
       shouldPass(1, inExclusiveRange(0,2));
       shouldFail(2, inExclusiveRange(0,2),
           "Expected: be in range from 0 (exclusive) to 2 (exclusive) "
-          "But: was <2>. Actual: <2>");
+          "Actual: <2>");
     });
 
     test('inOpenClosedRange', () {
       shouldFail(0, inOpenClosedRange(0,2),
           "Expected: be in range from 0 (exclusive) to 2 (inclusive) "
-          "But: was <0>. Actual: <0>");
+          "Actual: <0>");
       shouldPass(1, inOpenClosedRange(0,2));
       shouldPass(2, inOpenClosedRange(0,2));
     });
 
     test('inClosedOpenRange', () {
       shouldPass(0, inClosedOpenRange(0,2));
       shouldPass(1, inClosedOpenRange(0,2));
       shouldFail(2, inClosedOpenRange(0,2),
           "Expected: be in range from 0 (inclusive) to 2 (exclusive) "
-          "But: was <2>. Actual: <2>");
+          "Actual: <2>");
     });
   });
 
   group('String Matchers', () {
 
     test('isEmpty', () {
       shouldPass('', isEmpty);
       shouldFail(null, isEmpty,
-          "Expected: empty But: was <null>. Actual: <null>");
+          "Expected: empty Actual: <null>");
       shouldFail(0, isEmpty,
-          "Expected: empty But: was <0>. Actual: <0>");
-      shouldFail('a', isEmpty, "Expected: empty But: was 'a'. Actual: 'a'");
+          "Expected: empty Actual: <0>");
+      shouldFail('a', isEmpty, "Expected: empty Actual: 'a'");
     });
 
     test('equalsIgnoringCase', () {
       shouldPass('hello', equalsIgnoringCase('HELLO'));
       shouldFail('hi', equalsIgnoringCase('HELLO'),
-          "Expected: 'HELLO' ignoring case But: was 'hi'. Actual: 'hi'");
+          "Expected: 'HELLO' ignoring case Actual: 'hi'");
     });
 
     test('equalsIgnoringWhitespace', () {
       shouldPass(' hello   world  ', equalsIgnoringWhitespace('hello world'));
       shouldFail(' helloworld  ', equalsIgnoringWhitespace('hello world'),
           "Expected: 'hello world' ignoring whitespace "
-          "But: was 'helloworld'. Actual: ' helloworld '");
+          "Actual: ' helloworld ' "
+          "Which: is 'helloworld' with whitespace compressed");
     });
 
     test('startsWith', () {
       shouldPass('hello', startsWith(''));
       shouldPass('hello', startsWith('hell'));
       shouldPass('hello', startsWith('hello'));
       shouldFail('hello', startsWith('hello '),
           "Expected: a string starting with 'hello ' "
-          "But: was 'hello'. Actual: 'hello'");
+          "Actual: 'hello'");
     });
 
     test('endsWith', () {
       shouldPass('hello', endsWith(''));
       shouldPass('hello', endsWith('lo'));
       shouldPass('hello', endsWith('hello'));
       shouldFail('hello', endsWith(' hello'),
           "Expected: a string ending with ' hello' "
-          "But: was 'hello'. Actual: 'hello'");
+          "Actual: 'hello'");
     });
 
     test('contains', () {
       shouldPass('hello', contains(''));
       shouldPass('hello', contains('h'));
       shouldPass('hello', contains('o'));
       shouldPass('hello', contains('hell'));
       shouldPass('hello', contains('hello'));
       shouldFail('hello', contains(' '),
-          "Expected: contains ' ' But: was 'hello'. Actual: 'hello'");
+          "Expected: contains ' ' Actual: 'hello'");
     });
 
     test('stringContainsInOrder', () {
       shouldPass('goodbye cruel world', stringContainsInOrder(['']));
       shouldPass('goodbye cruel world', stringContainsInOrder(['goodbye']));
       shouldPass('goodbye cruel world', stringContainsInOrder(['cruel']));
       shouldPass('goodbye cruel world', stringContainsInOrder(['world']));
       shouldPass('goodbye cruel world',
                  stringContainsInOrder(['good', 'bye', 'world']));
       shouldPass('goodbye cruel world',
                  stringContainsInOrder(['goodbye', 'cruel']));
       shouldPass('goodbye cruel world',
                  stringContainsInOrder(['cruel', 'world']));
       shouldPass('goodbye cruel world',
         stringContainsInOrder(['goodbye', 'cruel', 'world']));
       shouldFail('goodbye cruel world',
         stringContainsInOrder(['goo', 'cruel', 'bye']),
         "Expected: a string containing 'goo', 'cruel', 'bye' in order "
-        "But: was 'goodbye cruel world'. Actual: 'goodbye cruel world'");
+        "Actual: 'goodbye cruel world'");
     });
 
     test('matches', () {
       shouldPass('c0d', matches('[a-z][0-9][a-z]'));
       shouldPass('c0d', matches(new RegExp('[a-z][0-9][a-z]')));
       shouldFail('cOd', matches('[a-z][0-9][a-z]'),
-          "Expected: match '[a-z][0-9][a-z]' But: was 'cOd'. Actual: 'cOd'");
+          "Expected: match '[a-z][0-9][a-z]' Actual: 'cOd'");
     });
   });
 
   group('Iterable Matchers', () {
 
     test('isEmpty', () {
       shouldPass([], isEmpty);
-      shouldFail([1], isEmpty, "Expected: empty But: was [1]. Actual: [1]");
+      shouldFail([1], isEmpty, "Expected: empty Actual: [1]");
     });
 
     test('contains', () {
       var d = [1, 2];
       shouldPass(d, contains(1));
       shouldFail(d, contains(0), "Expected: contains <0> "
-          "But: was [1, 2]. Actual: [1, 2]");
+          "Actual: [1, 2]");
     });
 
     test('isIn', () {
       var d = [1, 2];
       shouldPass(1, isIn(d));
-      shouldFail(0, isIn(d), "Expected: is in [1, 2] But: was <0>. Actual: <0>");
+      shouldFail(0, isIn(d), "Expected: is in [1, 2] Actual: <0>");
     });
 
     test('everyElement', () {
       var d = [1, 2];
       var e = [1, 1, 1];
       shouldFail(d, everyElement(1),
-          "Expected: every element <1> But: position 1 was <2>. "
-          "Actual: [1, 2]");
+          "Expected: every element <1> "
+          "Actual: [1, 2] "
+          "Which: at position 1 is <2>");
       shouldPass(e, everyElement(1));
     });
 
     test('someElement', () {
       var d = [1, 2];
       var e = [1, 1, 1];
       shouldPass(d, someElement(2));
       shouldFail(e, someElement(2),
-          "Expected: some element <2> But: was [1, 1, 1]. Actual: [1, 1, 1]");
+          "Expected: some element <2> Actual: [1, 1, 1]");
     });
 
     test('orderedEquals', () {
       shouldPass([null], orderedEquals([null]));
       var d = [1, 2];
       shouldPass(d, orderedEquals([1, 2]));
       shouldFail(d, orderedEquals([2, 1]),
           "Expected: equals [2, 1] ordered "
-          "But: expected <2> but was <1> mismatch at position 0. "
-          "Actual: [1, 2]");
+          "Actual: [1, 2] "
+          "Which: has mismatch at position 0: expected <2> but is <1>");
     });
 
     test('unorderedEquals', () {
       var d = [1, 2];
       shouldPass(d, unorderedEquals([2, 1]));
       shouldFail(d, unorderedEquals([1]),
           "Expected: equals [1] unordered "
-          "But: has too many elements (2 > 1). "
-          "Actual: [1, 2]");
+          "Actual: [1, 2] "
+          "Which: has too many elements (2 > 1)");
       shouldFail(d, unorderedEquals([3, 2, 1]),
           "Expected: equals [3, 2, 1] unordered "
-          "But: has too few elements (2 < 3). "
-          "Actual: [1, 2]");
+          "Actual: [1, 2] "
+          "Which: has too few elements (2 < 3)");
       shouldFail(d, unorderedEquals([3, 1]),
           "Expected: equals [3, 1] unordered "
-          "But: has no match for element <3> at position 0. "
-          "Actual: [1, 2]");
+          "Actual: [1, 2] "
+          "Which: has no match for element <3> at position 0");
     });
 
     test('pairwise compare', () {
       var c = [1, 2];
       var d = [1, 2, 3];
       var e = [1, 4, 9];
       shouldFail('x', pairwiseCompare(e, (e,a) => a <= e,
           "less than or equal"),
           "Expected: pairwise less than or equal [1, 4, 9] "
-          "But: not an Iterable. "
-          "Actual: 'x'");
+          "Actual: 'x' "
+          "Which: is not an Iterable");
       shouldFail(c, pairwiseCompare(e, (e,a) => a <= e, "less than or equal"),
           "Expected: pairwise less than or equal [1, 4, 9] "
-          "But: length was 2 instead of 3. "
-          "Actual: [1, 2]");
+          "Actual: [1, 2] "
+          "Which: has length 2 instead of 3");
       shouldPass(d, pairwiseCompare(e, (e,a) => a <= e, "less than or equal"));
       shouldFail(d, pairwiseCompare(e, (e,a) => a < e, "less than"),
           "Expected: pairwise less than [1, 4, 9] "
-          "But: <1> not less than <1> at position 0. "
-          "Actual: [1, 2, 3]");
+          "Actual: [1, 2, 3] "
+          "Which: has <1> which is not less than <1> at position 0");
       shouldPass(d, pairwiseCompare(e, (e,a) => a * a == e, "square root of"));
       shouldFail(d, pairwiseCompare(e, (e,a) => a + a == e, "double"),
           "Expected: pairwise double [1, 4, 9] "
-          "But: <1> not double <1> at position 0. "
-          "Actual: [1, 2, 3]");
+          "Actual: [1, 2, 3] "
+          "Which: has <1> which is not double <1> at position 0");
     });
   });
 
   group('Map Matchers', () {
 
     test('isEmpty', () {
       var a = new Map();
       shouldPass({}, isEmpty);
       shouldPass(a, isEmpty);
       a['foo'] = 'bar';
-      shouldFail(a, isEmpty, "Expected: empty But: was {'foo': 'bar'}. "
+      shouldFail(a, isEmpty, "Expected: empty "
           "Actual: {'foo': 'bar'}");
     });
 
     test('equals', () {
       var a = new Map();
       a['foo'] = 'bar';
       var b = new Map();
       b['foo'] = 'bar';
       var c = new Map();
       c['bar'] = 'foo';
       shouldPass(a, equals(b));
       shouldFail(b, equals(c),
-          "Expected: {'bar': 'foo'} But: missing map key 'bar'. "
-          "Actual: {'foo': 'bar'}");
+          "Expected: {'bar': 'foo'} "
+          "Actual: {'foo': 'bar'} "
+          "Which: is missing map key 'bar'");
     });
 
     test('equals with different lengths', () {
       var a = new LinkedHashMap();
       a['foo'] = 'bar';
       var b = new LinkedHashMap();
       b['foo'] = 'bar';
       b['bar'] = 'foo';
       var c = new LinkedHashMap();
       c['bar'] = 'foo';
       c['barrista'] = 'caffeine';
       shouldFail(a, equals(b),
           "Expected: {'foo': 'bar', 'bar': 'foo'} "
-          "But: different map lengths; missing map key 'bar'. "
-          "Actual: {'foo': 'bar'}");
+          "Actual: {'foo': 'bar'} "
+          "Which: has different length and is missing map key 'bar'");
       shouldFail(b, equals(a),
           "Expected: {'foo': 'bar'} "
-          "But: different map lengths; extra map key 'bar'. "
-          "Actual: {'foo': 'bar', 'bar': 'foo'}");
+          "Actual: {'foo': 'bar', 'bar': 'foo'} "
+          "Which: has different length and has extra map key 'bar'");
       shouldFail(b, equals(c),
           "Expected: {'bar': 'foo', 'barrista': 'caffeine'} "
-          "But: missing map key 'barrista'. "
-          "Actual: {'foo': 'bar', 'bar': 'foo'}");
+          "Actual: {'foo': 'bar', 'bar': 'foo'} "
+          "Which: is missing map key 'barrista'");
       shouldFail(c, equals(b),
           "Expected: {'foo': 'bar', 'bar': 'foo'} "
-          "But: missing map key 'foo'. "
-          "Actual: {'bar': 'foo', 'barrista': 'caffeine'}");
+          "Actual: {'bar': 'foo', 'barrista': 'caffeine'} "
+          "Which: is missing map key 'foo'");
       shouldFail(a, equals(c),
           "Expected: {'bar': 'foo', 'barrista': 'caffeine'} "
-          "But: different map lengths; missing map key 'bar'. "
-          "Actual: {'foo': 'bar'}");
+          "Actual: {'foo': 'bar'} "
+          "Which: has different length and is missing map key 'bar'");
       shouldFail(c, equals(a),
           "Expected: {'foo': 'bar'} "
-          "But: different map lengths; missing map key 'foo'. "
-          "Actual: {'bar': 'foo', 'barrista': 'caffeine'}");
+          "Actual: {'bar': 'foo', 'barrista': 'caffeine'} "
+          "Which: has different length and is missing map key 'foo'");
     });
 
     test('contains', () {
       var a = new Map();
       a['foo'] = 'bar';
       var b = new Map();
       shouldPass(a, contains('foo'));
       shouldFail(b, contains('foo'),
-          "Expected: contains 'foo' But: was {}. Actual: {}");
+          "Expected: contains 'foo' Actual: {}");
       shouldFail(10, contains('foo'),
-          "Expected: contains 'foo' But: was <10>. Actual: <10>");
+          "Expected: contains 'foo' Actual: <10>");
     });
 
     test('containsValue', () {
       var a = new Map();
       a['foo'] = 'bar';
       shouldPass(a, containsValue('bar'));
       shouldFail(a, containsValue('ba'),
-          "Expected: contains value 'ba' But: was {'foo': 'bar'}. "
+          "Expected: contains value 'ba' "
           "Actual: {'foo': 'bar'}");
     });
 
     test('containsPair', () {
       var a = new Map();
       a['foo'] = 'bar';
       shouldPass(a, containsPair('foo', 'bar'));
       shouldFail(a, containsPair('foo', 'ba'),
           "Expected: contains pair 'foo' => 'ba' "
-          "But: Strings are not equal. Both strings start the same, "
-          "but the given value also has the following trailing characters: r. "
-          "Actual: {'foo': 'bar'}");
+          "Actual: {'foo': 'bar'} "
+          "Which: is different. Both strings start the same, but "
+          "the given value also has the following trailing characters: r");
       shouldFail(a, containsPair('fo', 'bar'),
           "Expected: contains pair 'fo' => 'bar' "
-          "But: doesn't contain key 'fo'. "
-          "Actual: {'foo': 'bar'}");
+          "Actual: {'foo': 'bar'} "
+          "Which: doesn't contain key 'fo'");
     });
 
     test('hasLength', () {
       var a = new Map();
       a['foo'] = 'bar';
       var b = new Map();
       shouldPass(a, hasLength(1));
       shouldFail(b, hasLength(1),
           "Expected: an object with length of <1> "
-          "But: had length of <0>. "
-          "Actual: {}");
+          "Actual: {} "
+          "Which: has length of <0>");
     });
   });
 
   group('Operator Matchers', () {
 
     test('anyOf', () {
       shouldFail(0, anyOf([equals(1), equals(2)]),
-          "Expected: (<1> or <2>) But: was <0>. Actual: <0>");
+          "Expected: (<1> or <2>) Actual: <0>");
       shouldPass(1, anyOf([equals(1), equals(2)]));
     });
 
     test('allOf', () {
       shouldPass(1, allOf([lessThan(10), greaterThan(0)]));
       shouldFail(-1, allOf([lessThan(10), greaterThan(0)]),
           "Expected: (a value less than <10> and a value greater than <0>) "
-          "But: was <-1> (wasn't a value greater than <0>). Actual: <-1>");
+          "Actual: <-1> "
+          "Which: is not a value greater than <0>");
     });
   });
 
   group('Future Matchers', () {
 
     test('completes - unexpected error', () {
       var completer = new Completer();
       completer.completeError('X');
       shouldFail(completer.future, completes,
           contains('Expected future to complete successfully, '
@@ skipping 39 matching lines @@
     test('throwsA - correct error', () {
       var completer = new Completer();
       completer.completeError('X');
       shouldPass(completer.future, throwsA(equals('X')), isAsync: true);
     });
 
     test('throwsA - wrong error', () {
       var completer = new Completer();
       completer.completeError('X');
       shouldFail(completer.future, throwsA(equals('Y')),
-          "Expected: 'Y' But: Strings are not equal. "
-          "Expected: Y Actual: X ^ Differ at position 0. Actual: 'X'",
+          "Expected: 'Y' Actual: 'X' "
+          "Which: is different. "
+          "Expected: Y Actual: X ^ Differ at position 0",
           isAsync: true);
     });
   });
 
   group('Predicate Matchers', () {
     test('isInstanceOf', () {
       shouldFail(0, predicate((x) => x is String, "an instance of String"),
-          "Expected: an instance of String But: was <0>. Actual: <0>");
+          "Expected: an instance of String Actual: <0>");
       shouldPass('cow', predicate((x) => x is String, "an instance of String"));
     });
   });
 }