[tests] Rewrite the whole test suite to allow more granular testing.

Fix also a few bugs found while rewriting the test suite.

In order to be able to run integration tests, the test suite requires
a version of Redis >= 2.4.0.

The units have been splitted into several different groups using
PHPUnit @group annotation to allow developers to enable, disable
and combine certain types of tests. The available groups are:

  - disconnected: can run without a Redis server online
  - connected: active connection to a Redis server is required
  - commands: test dedicated to a specific Redis command
  - slow: performs operations that can slow down execution;

A list of the available groups can be obtained by running

  phpunit --list-groups

Groups of tests can be disabled or enabled via the XML configuration
file or the standard command-line test runner. Please note that due
to a bug in PHPUnit, older versions ignore the --group option when
the group is excluded in the XML configuration file. Please refer to
http://github.com/sebastianbergmann/phpunit/issues/320 for details

Integration tests in the @connected group check if the command being
tested is defined in the selected server profile (see the value of
the TEST_SERVER_VERSION constant in phpunit.xml). If the command is
not defined in the target server profile, the integration test is
automatically marked as skipped.

We also provide an helper script in the bin directory that can be
used to automatically generate a file with the scheleton of a test
case for a Redis command by specifying the name of the class in the
Predis\Commands namespace. For example, to generate a test case for
SET (represented by the Predis\Commands\StringSet class):

  ./bin/generate-command-test.php --class=StringSet

The realm of a command is automatically inferred from the name of the
class, but it can be set using the --realm option.

lib/Predis/Transaction/MultiExecContext.php

@@ -16,6 +16,7 @@ use Predis\Helpers;
 use Predis\ResponseQueued;
 use Predis\ClientException;
 use Predis\ServerException;
+use Predis\NotSupportedException;
 use Predis\CommunicationException;
 use Predis\Protocol\ProtocolException;
 
@@ -112,17 +113,12 @@ class MultiExecContext
     private function checkCapabilities(Client $client)
     {
         if (Helpers::isCluster($client->getConnection())) {
-            throw new ClientException(
-                'Cannot initialize a MULTI/EXEC context over a cluster of connections'
-            );
+            throw new NotSupportedException('Cannot initialize a MULTI/EXEC context over a cluster of connections');
         }
 
         $profile = $client->getProfile();
-
         if ($profile->supportsCommands(array('multi', 'exec', 'discard')) === false) {
-            throw new ClientException(
-                'The current profile does not support MULTI, EXEC and DISCARD'
-            );
+            throw new NotSupportedException('The current profile does not support MULTI, EXEC and DISCARD');
         }
 
         $this->canWatch = $profile->supportsCommands(array('watch', 'unwatch'));
@@ -134,9 +130,7 @@ class MultiExecContext
     private function isWatchSupported()
     {
         if ($this->canWatch === false) {
-            throw new ClientException(
-                'The current profile does not support WATCH and UNWATCH'
-            );
+            throw new NotSupportedException('The current profile does not support WATCH and UNWATCH');
         }
     }
 
@@ -256,7 +250,7 @@ class MultiExecContext
     {
         $this->isWatchSupported();
         $this->unflagState(self::STATE_WATCH);
-        $this->client->unwatch();
+        $this->__call('unwatch', array());
 
         return $this;
     }
@@ -297,31 +291,23 @@ class MultiExecContext
     private function checkBeforeExecution($callable)
     {
         if ($this->checkState(self::STATE_INSIDEBLOCK)) {
-            throw new ClientException(
-                "Cannot invoke 'execute' or 'exec' inside an active client transaction block"
-            );
+            throw new ClientException("Cannot invoke 'execute' or 'exec' inside an active client transaction block");
         }
 
         if ($callable) {
             if (!is_callable($callable)) {
-                throw new \InvalidArgumentException(
-                    'Argument passed must be a callable object'
-                );
+                throw new \InvalidArgumentException('Argument passed must be a callable object');
             }
 
             if (count($this->commands) > 0) {
                 $this->discard();
-                throw new ClientException(
-                    'Cannot execute a transaction block after using fluent interface'
-                );
+                throw new ClientException('Cannot execute a transaction block after using fluent interface');
             }
         }
 
         if (isset($this->options['retry']) && !isset($callable)) {
             $this->discard();
-            throw new \InvalidArgumentException(
-                'Automatic retries can be used only when a transaction block is provided'
-            );
+            throw new \InvalidArgumentException('Automatic retries can be used only when a transaction block is provided');
         }
     }