Added channel setter for tests

[chimit]

Currently, there is only one way to set recipient (channel) in tests by instantiating the IncomingMessage class:

$incoming1 = new IncomingMessage('hi', $sender, $recipient, ['foo' => 'bar']);
$incoming2 = new IncomingMessage('good', $sender, $recipient, ['foo' => 'bar']);

$this->bot
    ->setUser($sender)
    ->receivesRaw($incoming1)
    ->assertQuestion('How are you?')
    ->receivesRaw($incoming2);

This PR adds an ability to make it easier through a setChannel setter:

$this->bot
    ->setUser($sender)
    ->setChannel($channel)
    ->receives('hi', ['foo' => 'bar'])
    ->assertQuestion('How are you?')
    ->receives('good', ['foo' => 'bar']);

It's really useful in conversations. Otherwise, you should instantiate IncomingMessage for every message in a conversation.

Partially solves this issue https://github.com/botman/botman/issues/1218

[codecov[bot]]

Codecov Report

Base: 43.35% // Head: 43.88% // Increases project coverage by +0.53% :tada:

Coverage data is based on head (a454ec0) compared to base (1b6cf1b). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #51      +/-   ##
============================================
+ Coverage     43.35%   43.88%   +0.53%     
- Complexity       75       76       +1     
============================================
  Files            11       11              
  Lines           316      319       +3     
============================================
+ Hits            137      140       +3     
  Misses          179      179              

Impacted Files	Coverage Δ
src/Testing/BotManTester.php	95.62% <100.00%> (+0.09%)	:arrow_up:

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[chimit]

@crynobone @mpociot any chances to get this merged?

[chimit]

@christophrumpel can this tiny fix be merged?