Initial version of mocking support. There is still quite a bit of

lib/unittest/mock.dart

Index: lib/unittest/mock.dart
===================================================================
--- lib/unittest/mock.dart	(revision 0)
+++ lib/unittest/mock.dart	(revision 0)
@@ -0,0 +1,435 @@
+// 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.
+
+/**
+ * Support for basic mocking.
+ *
+ * To create a mock objects for some class T, create a new class using:
+ *
+ *     class MockT extends Mock implements T {};
+ *
+ * Then specify the behavior of the Mock for different methods using
+ * [when] (to select the method and parameters) and [thenReturn],
+ * [alwaysReturn], [thenThrow] and/or [alwaysThrow].
+ *
+ * You can then use the mock object. Once you are done, to verify the
+ * behavior, use [verify] to extract a relevant subset of method call
+ * logs and apply [Matchers] to these.
+ *
+ * Limitations:
+ * - only positional parameters are supported (up to 10);
+ * - to mock getters you will need to include parentheses.
+ *
+ * Here is a simple example:
+ *
+ *     class MockList extends Mock implements List {};
+ *
+ *     List m = new MockList();
+ *     m.when('add', anything).alwaysReturn(0);
+ *
+ *     m.add('foo');
+ *     m.add('bar');
+ *
+ *     m.verify('add', anything, was:calledExactly(2));
+ *     m.verify('add', 'foo', was:calledOnce);
+ *     m.verify('add', 'isNull, was:neverCalled);
+ */
+

[Siggi Cherem (dart-lang), 2012/06/26 21:35:44]

maybe this should be it's own library?
#library('mock');

[gram, 2012/06/26 23:39:59]

I thought about that, but I think that as long as we keep the matchers in
unittest we may as well put mock in too. Alternatively we should separate these
into three, unittest, matchers and mock.

[Siggi Cherem (dart-lang), 2012/06/26 23:58:27]

Then it would be nice if this documentation is attached to something so that
will make it visible in api.dartlang.org. Maybe move it down and make it the
dartdoc of the Mock class?

+/**
+ * The error formatter for mocking is a bit different from the default one
+ * for unit testing; instead of the third argument being a 'reason'
+ * it is instead a [signature] describing the method signature filter
+ * that was used to select the logs that were verified.
+ */
+

[Siggi Cherem (dart-lang), 2012/06/26 21:35:44]

remove empty line

[gram, 2012/06/26 23:39:59]

Done.

+String _mockingErrorFormatter(actual, Matcher matcher, String signature) {
+  var description = new StringDescription();
+  description.add('Expected ${signature} ').addDescriptionOf(matcher).
+      add('\n     but: ');
+  matcher.describeMismatch(actual, description);
+  return description.toString();
+}
+
+/**
+ * The failure handler for the [expect()] calls that occur in [verify()]
+ * methods in the mock objects. This calls the real failure handler used
+ * by the unit test library after formatting the error message with
+ * the custom formatter.
+ */
+class _MockFailureHandler implements FailureHandler {
+  FailureHandler proxy;
+  _MockFailureHandler(this.proxy);
+  void fail(String reason) {
+    proxy.fail(reason);
+  }
+  void failMatch(actual, Matcher matcher, String reason) {
+    proxy.fail(_mockingErrorFormatter(actual, matcher, reason));
+  }
+}
+
+_MockFailureHandler _mockFailureHandler = null;
+
+/**
+ * [_NoArg] is a class with an instance used to fake varargs.
+ */
+class _NoArg {

[Siggi Cherem (dart-lang), 2012/06/26 21:35:44]

we are also doing the same thing for _SpreadArgsHelper. Can we share some of
this code. Maybe share the _Sentinel/_NoArg types?

[gram, 2012/06/26 23:39:59]

Done.

+  const _NoArg();
+  String toString() => '';
+}
+
+/**
+ * [noArg] is a sentinel value representing no argument.
+ */
+final noArg = const _NoArg();

[Siggi Cherem (dart-lang), 2012/06/26 21:35:44]

=> _noArg (make noArg private to this library.)

[gram, 2012/06/26 23:39:59]

Done.

+
+/**
+ * The behavior of a method call in the mock library is specified
+ * with [BehaviorValue]s. A [BehaviorValue] has a [value] to throw
+ * or return (depending on whether [isThrow] is true or not, respectively),
+ * and can either be one-shot or repeating, depending on the value of
+ * of [isOneShot].
+ */
+class BehaviorValue {
+  var value;
+  bool isThrow;
+  bool isOneShot;

[Siggi Cherem (dart-lang), 2012/06/26 21:35:44]

maybe instead of 1 vs many, could we specify a number of times? For instance:
m.when('foo', 3).thenReturn(3, count: 3);

would be equivalent to:
m.when('foo', 3).thenReturn(3);
m.when('foo', 3).thenReturn(3);
m.when('foo', 3).thenReturn(3);

[gram, 2012/06/26 23:39:59]

Done.

+  BehaviorValue(this.value, [this.isOneShot = true, this.isThrow = false]);
+}
+
+/**
+ * A [CallMatcher] is a special matcher used to match method calls (i.e.
+ * a method name and set of arguments). It is not a [Matcher] like the
+ * unit test [Matcher], but instead represents a collection of [Matcher]s,
+ * one per argument, that will be applied to the parameters to decide if
+ * the method call is a match.
+ */
+class CallMatcher {
+  String name;
+  List<Matcher> argMatchers;
+
+  CallMatcher(String method, [
+              arg0 = noArg,
+              arg1 = noArg,
+              arg2 = noArg,
+              arg3 = noArg,
+              arg4 = noArg,
+              arg5 = noArg,
+              arg6 = noArg,
+              arg7 = noArg,
+              arg8 = noArg,
+              arg9 = noArg]) {
+    name = method;
+    argMatchers = new List<Matcher>();
+    if (arg0 != noArg) {
+      argMatchers.add(wrapMatcher(arg0));
+      if (arg1 != noArg) {
+        argMatchers.add(wrapMatcher(arg1));
+        if (arg2 != noArg) {
+          argMatchers.add(wrapMatcher(arg2));
+          if (arg3 != noArg) {
+            argMatchers.add(wrapMatcher(arg3));
+            if (arg4 != noArg) {
+              argMatchers.add(wrapMatcher(arg4));
+              if (arg5 != noArg) {
+                argMatchers.add(wrapMatcher(arg5));
+                if (arg6 != noArg) {
+                  argMatchers.add(wrapMatcher(arg6));
+                  if (arg7 != noArg) {
+                    argMatchers.add(wrapMatcher(arg7));
+                    if (arg8 != noArg) {
+                      argMatchers.add(wrapMatcher(arg8));
+                      if (arg9 != noArg) {
+                        argMatchers.add(wrapMatcher(arg9));

[Siggi Cherem (dart-lang), 2012/06/26 21:35:44]

style nit: pine trees!! please fix

[gram, 2012/06/26 23:39:59]

Done.

+                      }
+                    }
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+
+  /**
+   * We keep our behavior specifications in a Map, which is keyed
+   * by the [CallMatcher]. To make the keys unique and to get a
+   * descriptive value for the [CallMatcher] we have this override
+   * of [toString()].
+   */
+  String toString() {
+    Description d = new StringDescription();
+    d.add(name).add('(');
+    for (var i = 0; i < argMatchers.length; i++) {
+      if (i > 0) d.add(', ');
+      d.addDescriptionOf(argMatchers[i]);
+    }
+    d.add(')');
+    return d.toString();
+  }
+
+  /**
+   * Given a [method] name oand list of [arguments], return true
+   * if it matches this [CallMatcher.
+   */
+  bool matches(String method, List arguments) {
+    if (method != this.name || arguments.length != argMatchers.length) {
+      return false;
+    }
+    for (var i = 0; i < arguments.length; i++) {
+      if (!argMatchers[i].matches(arguments[i])) {
+        return false;
+      }
+    }
+    return true;
+  }
+}
+
+/**
+ * A [Behavior] represents how a [Mock] will respond to one particular
+ * type of method call.
+ */
+class Behavior {
+  CallMatcher matcher; // The method call matcher.
+  List<BehaviorValue> returnValues; // The values to return/throw.
+
+  Behavior (this.matcher) {
+    returnValues = new List<BehaviorValue>();
+  }
+
+  /** [thenReturn] creates a one-shot return value. */
+  Behavior thenReturn(value) {

[Siggi Cherem (dart-lang), 2012/06/26 21:35:44]

=> consider adding a count parameter ?

[gram, 2012/06/26 23:39:59]

Done.

+    returnValues.add(new BehaviorValue(value));
+    return this; // For chaining calls.
+  }
+
+  /** [alwaysReturn] creates a repeating return value. */
+  Behavior alwaysReturn(value) {
+    returnValues.add(new BehaviorValue(value, false));
+    return this; // For chaining calls.
+  }
+
+  /** [thenThrow] creates a one-shot exception. */
+  Behavior thenThrow(value) {
+    returnValues.add(new BehaviorValue(value, true, true));
+    return this; // For chaining calls.
+  }
+
+  /** [alwaysThrow] creates a repeating exception. */
+  Behavior alwaysThrow(value) {
+    returnValues.add(new BehaviorValue(value, false, true));
+    return this; // For chaining calls.
+  }
+
+  /** [matches] return true if a method call matches the [Behavior]. */
+  bool matches(name, args) => matcher.matches(name, args);
+}
+
+/**
+ * Every call to a [Mock] object method is logged. The logs are
+ * kept in instances of [LogEntry].
+ */
+class LogEntry {
+  final String name; // The method name.
+  final List args; // The parameters.
+  final BehaviorValue result; // The behavior that resulted.
+
+  const LogEntry(this.name, this.args, this.result);
+}
+
+/**
+ * We do verification on a list of [LogEntry]s. To allow chaining
+ * of calls to verify, we encapsulate such a list in the [LogEntryList]
+ * class.
+ */
+class LogEntryList {

[Siggi Cherem (dart-lang), 2012/06/26 21:35:44]

implements/extends List<LogEntry>? 

[gram, 2012/06/26 23:39:59]

You can't use extends like that, only implements, which is not that useful.

+  final String filter;
+  final List<LogEntry> logs;
+  const LogEntryList(this.logs, [this.filter = null]);
+
+  /** Add a [LogEntry] to the log. */
+  void add(LogEntry entry) {
+    logs.add(entry);
+  }
+
+  /**
+   * Create a new [LogEntryList] consisting of [LogEntry]s from
+   * this list that match the specified [logfilter].
+   */
+  LogEntryList getMatches(CallMatcher logfilter) {
+    LogEntryList rtn =
+        new LogEntryList(new List<LogEntry>(), logfilter.toString());
+    for (var i = 0; i < logs.length; i++) {
+      LogEntry entry = logs[i];
+      if (logfilter.matches(entry.name, entry.args)) {
+        rtn.add(entry);
+      }
+    }
+    return rtn;
+  }
+
+  /** Apply a unit test [Matcher] to the [LogEntryList]. */
+  LogEntryList verify(Matcher matcher) {
+    if (_mockFailureHandler == null) {
+      _mockFailureHandler = new _MockFailureHandler(getFailureHandler());
+    }
+    expect(logs, matcher, filter, _mockFailureHandler);
+    return this;
+  }
+}
+
+/**
+ * [_TimesMatcher]s are used to make assertions about the number of
+ * times a method was called.
+ */
+class _TimesMatcher extends BaseMatcher {
+  final int min, max;
+  const _TimesMatcher(this.min, [this.max = -1]);
+  bool matches(log) => log.length >= min && (max < 0 || log.length <= max);
+  Description describe(Description description) {
+    description.add(' to be called ');
+    if (max < 0) {
+      description.add('at least $min');
+    } else if (max == min) {
+      description.add('$max');
+    } else if (min == 0) {
+      description.add('at most $max');
+    } else {
+      description.add('between $min and $max');
+    }
+    return description.add(' times');
+  }
+  Description describeMismatch(log, Description mismatchDescription) =>
+      mismatchDescription.add('was called ${log.length} times');
+}
+
+/** [calledExactly] matches an exact number of calls. */
+Matcher calledExactly(count) {
+  return new _TimesMatcher(count, count);
+}
+
+/** [calledAtLeast] matches a minimum number of calls. */
+Matcher calledAtLeast(count) {
+  return new _TimesMatcher(count);
+}
+
+/** [calledAtMost] matches a maximum number of calls. */
+Matcher calledAtMost(count) {
+  return new _TimesMatcher(0, count);
+}
+
+/** [neverCalled] matches zero calls. */
+final Matcher neverCalled = const _TimesMatcher(0, 0);
+
+/** [calledOnce] matches exactly one call. */
+final Matcher calledOnce = const _TimesMatcher(1, 1);
+
+/** [calledAtLeastOnce] matches one or more calls. */
+final Matcher calledAtLeastOnce = const _TimesMatcher(1);
+
+/** [calledAtMostOnce] matches zero or one call. */
+final Matcher calledAtMostOnce = const _TimesMatcher(0, 1);
+
+/** [Mock] is the base class for all mocked objects. */
+class Mock {
+  Map<String,Behavior> behaviors; /** The set of [behavior]s supported. */
+  LogEntryList log; /** The [log] of calls made. */
+
+  Mock() {
+    behaviors = new Map<String,Behavior>();
+    log = new LogEntryList(new List<LogEntry>());
+  }
+
+  /**
+   * [when] is used to create a new or extend an existing [Behavior].
+   * The [method] name and the argument [Matcher] is specified. A
+   * corresponding [CallMatcher] is created, and the [Behavior]s for
+   * its signature are returned (being created first if needed).
+   */
+  Behavior when(String method, [
+       arg0 = noArg,
+       arg1 = noArg,
+       arg2 = noArg,
+       arg3 = noArg,
+       arg4 = noArg,
+       arg5 = noArg,
+       arg6 = noArg,
+       arg7 = noArg,
+       arg8 = noArg,
+       arg9 = noArg]) {
+    CallMatcher logfilter = new CallMatcher(method,
+        arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9);
+    String key = logfilter.toString();
+    if (!behaviors.containsKey(key)) {
+      Behavior b = new Behavior(logfilter);
+      behaviors[key] = b;
+      return b;
+    } else {
+      return behaviors[key];
+    }
+  }
+
+  /**
+   * This is the handler for method calls. We loo through the list
+   * of [Behavior]s, and find the first match that still has return
+   * values available, and then do the action specified by that
+   * return value. If we find no [Behavior] to apply an exception is
+   * thrown.
+   */
+  noSuchMethod(String name, List args) {
+    for (Behavior b in behaviors.getValues()) {
+      if (b.matches(name, args)) {
+        List rv = b.returnValues;
+        if (rv == null || rv.length == 0) {
+          continue; // No return values left in this Behavior.

[Siggi Cherem (dart-lang), 2012/06/26 21:35:44]

should we do some cleanup of the behaviour list if this rv is no longer useful
anymore (e.g. remove an rv that is a one-shot after it's used?

[gram, 2012/06/26 23:39:59]

Maybe, maybe not. If perf was an issue we could move exhausted behaviors to
another list. But it seems to me there may be some value in keeping the
behaviors around, so we know which behaviors were exercised how many times.
Nonetheless, right now we aree not using it so I am going to take your advice,
remove it, and add a comment.

[Siggi Cherem (dart-lang), 2012/06/26 23:58:27]

Ok - I'm also not sure what are the performance implications of doing the
removal (since removal is linear in list implementations)

+        }
+        // Get the first response.
+        BehaviorValue bv = rv[0];
+        // If it is one-shot, remove it from the list.
+        if (bv.isOneShot) {
+          rv.removeRange(0, 1);
+        }
+        // Log the method call and the response.
+        log.add(new LogEntry(name, args, bv));
+        // Do the response.
+        if (bv.isThrow) {
+          throw bv.value;
+        } else {
+          return bv.value;
+        }
+      }
+    }
+    throw new Exception('No behavior specified for method $name');
+  }
+
+  /**
+   * [verify] extracts all calls from the object log that match the
+   * method signature, then applies the [was] matcher. The matching
+   * list of [LogEntry]s is returned so that further calls to verify()
+   * can be chained .
+   */
+  LogEntryList verify(String method, [ arg0 = noArg,
+                          arg1 = noArg,
+                          arg2 = noArg,
+                          arg3 = noArg,
+                          arg4 = noArg,
+                          arg5 = noArg,
+                          arg6 = noArg,
+                          arg7 = noArg,
+                          arg8 = noArg,
+                          arg9 = noArg,
+                          Matcher was = calledOnce]) {
+    CallMatcher logfilter = new CallMatcher(method,
+      arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9);
+    LogEntryList _logs = log.getMatches(logfilter);
+    _logs.verify(was);
+    return _logs;
+  }
+
+  /** [verifyZeroInteractions] returns true if no calls were made */
+  bool verifyZeroInteractions() => log.logs.length == 0;
+
+}
+