diff --git a/modules/monitoring/library/Monitoring/MonitoringWizard.php b/modules/monitoring/library/Monitoring/MonitoringWizard.php
index e746db0338..6399862461 100644
--- a/modules/monitoring/library/Monitoring/MonitoringWizard.php
+++ b/modules/monitoring/library/Monitoring/MonitoringWizard.php
@@ -148,9 +148,10 @@ public function getRequirements()
             )
         )));
 
-        $idoSet = new RequirementSet(RequirementSet::MODE_OR);
-        $mysqlSet = new RequirementSet();
+        $idoSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $mysqlSet = new RequirementSet(true);
         $mysqlSet->add(new PhpModuleRequirement(array(
+            'optional'      => true,
             'condition'     => 'mysql',
             'alias'         => 'PDO-MySQL',
             'description'   => mt(
@@ -159,6 +160,7 @@ public function getRequirements()
             )
         )));
         $mysqlSet->add(new ClassRequirement(array(
+            'optional'      => true,
             'condition'     => 'Zend_Db_Adapter_Pdo_Mysql',
             'alias'         => mt('monitoring', 'Zend database adapter for MySQL'),
             'description'   => mt(
@@ -167,8 +169,9 @@ public function getRequirements()
             )
         )));
         $idoSet->merge($mysqlSet);
-        $pgsqlSet = new RequirementSet();
+        $pgsqlSet = new RequirementSet(true);
         $pgsqlSet->add(new PhpModuleRequirement(array(
+            'optional'      => true,
             'condition'     => 'pgsql',
             'alias'         => 'PDO-PostgreSQL',
             'description'   => mt(
@@ -177,6 +180,7 @@ public function getRequirements()
             )
         )));
         $pgsqlSet->add(new ClassRequirement(array(
+            'optional'      => true,
             'condition'     => 'Zend_Db_Adapter_Pdo_Pgsql',
             'alias'         => mt('monitoring', 'Zend database adapter for PostgreSQL'),
             'description'   => mt(
diff --git a/modules/setup/library/Setup/RequirementSet.php b/modules/setup/library/Setup/RequirementSet.php
index 6ffce61fb7..966cf98ccc 100644
--- a/modules/setup/library/Setup/RequirementSet.php
+++ b/modules/setup/library/Setup/RequirementSet.php
@@ -12,17 +12,31 @@
 class RequirementSet implements RecursiveIterator
 {
     /**
-     * Mode AND (all requirements must met)
+     * Mode AND (all requirements must be met)
      */
     const MODE_AND = 0;
 
     /**
-     * Mode OR (at least one requirement must met)
+     * Mode OR (at least one requirement must be met)
      */
     const MODE_OR = 1;
 
     /**
-     * The mode by with the requirements are evaluated
+     * Whether all requirements meet their condition
+     *
+     * @var bool
+     */
+    protected $state;
+
+    /**
+     * Whether this set is optional
+     *
+     * @var bool
+     */
+    protected $optional;
+
+    /**
+     * The mode by which the requirements are evaluated
      *
      * @var string
      */
@@ -36,26 +50,75 @@ class RequirementSet implements RecursiveIterator
     protected $requirements;
 
     /**
-     * Whether there is any mandatory requirement part of this set
+     * The raw state of this set's requirements
      *
      * @var bool
      */
-    protected $containsMandatoryRequirements;
+    private $forcedState;
 
     /**
-     * Create a new set of requirements
+     * Initialize a new set of requirements
      *
-     * @param   int     $mode   The mode by with to evaluate the requirements
+     * @param   bool    $optional   Whether this set is optional
+     * @param   int     $mode       The mode by which to evaluate this set
      */
-    public function __construct($mode = null)
+    public function __construct($optional = false, $mode = null)
     {
+        $this->optional = $optional;
         $this->requirements = array();
-        $this->containsMandatoryRequirements = false;
         $this->setMode($mode ?: static::MODE_AND);
     }
 
     /**
-     * Set the mode by with to evaluate the requirements
+     * Set the state of this set
+     *
+     * @param   bool    $state
+     *
+     * @return  RequirementSet
+     */
+    public function setState($state)
+    {
+        $this->state = (bool) $state;
+        return $this;
+    }
+
+    /**
+     * Return the state of this set
+     *
+     * Alias for RequirementSet::fulfilled(true).
+     *
+     * @return  bool
+     */
+    public function getState()
+    {
+        return $this->fulfilled(true);
+    }
+
+    /**
+     * Set whether this set of requirements should be optional
+     *
+     * @param   bool    $state
+     *
+     * @return  RequirementSet
+     */
+    public function setOptional($state = true)
+    {
+        $this->optional = (bool) $state;
+        return $this;
+    }
+
+    /**
+     * Return whether this set of requirements is optional
+     *
+     * @return  bool
+     */
+    public function isOptional()
+    {
+        return $this->optional;
+    }
+
+    /**
+     * Set the mode by which to evaluate the requirements
      *
      * @param   int     $mode
      *
@@ -74,7 +137,7 @@ public function setMode($mode)
     }
 
     /**
-     * Return the mode by with the requirements are evaluated
+     * Return the mode by which the requirements are evaluated
      *
      * @return  int
      */
@@ -95,10 +158,7 @@ public function add(Requirement $requirement)
         $merged = false;
         foreach ($this->requirements as $knownRequirement) {
             if ($knownRequirement instanceof Requirement && $requirement->equals($knownRequirement)) {
-                if ($this->getMode() === static::MODE_AND && !$requirement->isOptional()) {
-                    $knownRequirement->setOptional(false);
-                }
-
+                $knownRequirement->setOptional($requirement->isOptional());
                 foreach ($requirement->getDescriptions() as $description) {
                     $knownRequirement->addDescription($description);
                 }
@@ -109,12 +169,6 @@ public function add(Requirement $requirement)
         }
 
         if (! $merged) {
-            if ($this->getMode() === static::MODE_OR) {
-                $requirement->setOptional();
-            } elseif (! $requirement->isOptional()) {
-                $this->containsMandatoryRequirements = true;
-            }
-
             $this->requirements[] = $requirement;
         }
 
@@ -132,25 +186,15 @@ public function getAll()
     }
 
     /**
-     * Return whether there is any mandatory requirement part of this set
-     *
-     * @return  bool
-     */
-    public function hasAnyMandatoryRequirement()
-    {
-        return $this->containsMandatoryRequirements || $this->getMode() === static::MODE_OR;
-    }
-
-    /**
-     * Register the given requirements
+     * Register the given set of requirements
      *
-     * @param   RequirementSet  $set    The requirements to register
+     * @param   RequirementSet  $set    The set to register
      *
      * @return  RequirementSet
      */
     public function merge(RequirementSet $set)
     {
-        if ($this->getMode() === static::MODE_OR && $set->getMode() === static::MODE_OR) {
+        if ($this->getMode() === $set->getMode() && $this->isOptional() === $set->isOptional()) {
             foreach ($set->getAll() as $requirement) {
                 if ($requirement instanceof static) {
                     $this->merge($requirement);
@@ -159,10 +203,6 @@ public function merge(RequirementSet $set)
                 }
             }
         } else {
-            if ($set->getMode() === static::MODE_OR) {
-                $this->containsMandatoryRequirements = true;
-            }
-
             $this->requirements[] = $set;
         }
 
@@ -172,40 +212,45 @@ public function merge(RequirementSet $set)
     /**
      * Return whether all requirements can successfully be evaluated based on the current mode
      *
+     * In case this is a optional set of requirements (and $force is false), true is returned immediately.
+     *
+     * @param   bool    $force      Whether to ignore the optionality of a set or single requirement
+     *
      * @return  bool
      */
-    public function fulfilled()
+    public function fulfilled($force = false)
     {
-        $state = false;
-        foreach ($this->requirements as $requirement) {
-            if ($requirement instanceof static) {
-                if ($requirement->fulfilled()) {
-                    if ($this->getMode() === static::MODE_OR) {
-                        return true;
-                    }
-
-                    $state = true;
-                } elseif ($this->getMode() === static::MODE_AND && $requirement->hasAnyMandatoryRequirement()) {
-                    return false;
+        $state = $this->isOptional();
+        if (! $force && $state) {
+            return true;
+        }
+
+        if (! $force && $this->state !== null) {
+            return $this->state;
+        } elseif ($force && $this->forcedState !== null) {
+            return $this->forcedState;
+        }
+
+        $self = $this->requirements;
+        foreach ($self as $requirement) {
+            if ($requirement->getState()) {
+                $state = true;
+                if ($this->getMode() === static::MODE_OR) {
+                    break;
                 }
-            } else {
-                if ($requirement->getState()) {
-                    if ($this->getMode() === static::MODE_OR) {
-                        return true;
-                    }
-
-                    $state = true;
-                } elseif ($this->getMode() === static::MODE_AND) {
-                    if (! $requirement->isOptional()) {
-                        return false;
-                    }
-
-                    $state = true; // There may only be optional requirements...
+            } elseif ($force || !$requirement->isOptional()) {
+                $state = false;
+                if ($this->getMode() === static::MODE_AND) {
+                    break;
                 }
             }
         }
 
-        return $state;
+        if ($force) {
+            return $this->forcedState = $state;
+        }
+
+        return $this->state = $state;
     }
 
     /**
diff --git a/modules/setup/library/Setup/WebWizard.php b/modules/setup/library/Setup/WebWizard.php
index d3bb71bfa4..e3091bd4d2 100644
--- a/modules/setup/library/Setup/WebWizard.php
+++ b/modules/setup/library/Setup/WebWizard.php
@@ -451,7 +451,7 @@ public function getRequirements()
             )
         )));
 
-        $mysqlSet = new RequirementSet();
+        $mysqlSet = new RequirementSet(true);
         $mysqlSet->add(new PhpModuleRequirement(array(
             'optional'      => true,
             'condition'     => 'mysql',
@@ -472,7 +472,7 @@ public function getRequirements()
         )));
         $set->merge($mysqlSet);
 
-        $pgsqlSet = new RequirementSet();
+        $pgsqlSet = new RequirementSet(true);
         $pgsqlSet->add(new PhpModuleRequirement(array(
             'optional'      => true,
             'condition'     => 'pgsql',
diff --git a/modules/setup/test/php/library/Setup/RequirementSetTest.php b/modules/setup/test/php/library/Setup/RequirementSetTest.php
new file mode 100644
index 0000000000..d2c4d20291
--- /dev/null
+++ b/modules/setup/test/php/library/Setup/RequirementSetTest.php
@@ -0,0 +1,496 @@
+<?php
+/* Icinga Web 2 | (c) 2013-2015 Icinga Development Team | GPLv2+ */
+
+namespace Tests\Icinga\Module\Setup;
+
+use Icinga\Test\BaseTestCase;
+use Icinga\Module\Setup\Requirement;
+use Icinga\Module\Setup\RequirementSet;
+
+class TrueRequirement extends Requirement
+{
+    protected function evaluate()
+    {
+        return true;
+    }
+}
+
+class FalseRequirement extends Requirement
+{
+    protected function evaluate()
+    {
+        return false;
+    }
+}
+
+class RequirementSetTest extends BaseTestCase
+{
+    public function testFlatMandatoryRequirementsOfTypeAnd()
+    {
+        $emptySet = new RequirementSet();
+        $this->assertFalse($emptySet->fulfilled(), 'A empty mandatory set of type and is fulfilled');
+
+        $singleTrueSet = new RequirementSet();
+        $singleTrueSet->add(new TrueRequirement());
+        $this->assertTrue(
+            $singleTrueSet->fulfilled(),
+            'A mandatory set of type and with a single TrueRequirement is not fulfilled'
+        );
+
+        $singleFalseSet = new RequirementSet();
+        $singleFalseSet->add(new FalseRequirement());
+        $this->assertFalse(
+            $singleFalseSet->fulfilled(),
+            'A mandatory set of type and with a single FalseRequirement is fulfilled'
+        );
+
+        $mixedSet = new RequirementSet();
+        $mixedSet->add(new TrueRequirement());
+        $mixedSet->add(new FalseRequirement());
+        $this->assertFalse(
+            $mixedSet->fulfilled(),
+            'A mandatory set of type and with one True- and one FalseRequirement is fulfilled'
+        );
+    }
+
+    public function testFlatOptionalRequirementsOfTypeAnd()
+    {
+        $emptySet = new RequirementSet(true);
+        $this->assertTrue($emptySet->fulfilled(), 'A empty optional set of type and is not fulfilled');
+
+        $singleTrueSet = new RequirementSet(true);
+        $singleTrueSet->add(new TrueRequirement());
+        $this->assertTrue(
+            $singleTrueSet->fulfilled(),
+            'A optional set of type and with a single TrueRequirement is not fulfilled'
+        );
+
+        $singleFalseSet = new RequirementSet(true);
+        $singleFalseSet->add(new FalseRequirement());
+        $this->assertTrue(
+            $singleFalseSet->fulfilled(),
+            'A optional set of type and with a single FalseRequirement is not fulfilled'
+        );
+
+        $mixedSet = new RequirementSet(true);
+        $mixedSet->add(new TrueRequirement());
+        $mixedSet->add(new FalseRequirement());
+        $this->assertTrue(
+            $mixedSet->fulfilled(),
+            'A optional set of type and with one True- and one FalseRequirement is not fulfilled'
+        );
+    }
+
+    public function testFlatMixedRequirementsOfTypeAnd()
+    {
+        $mandatoryOptionalTrueSet = new RequirementSet();
+        $mandatoryOptionalTrueSet->add(new TrueRequirement(array('optional' => true)));
+        $mandatoryOptionalTrueSet->add(new FalseRequirement());
+        $this->assertFalse(
+            $mandatoryOptionalTrueSet->fulfilled(),
+            'A mandatory set of type and with one optional True- and one mandatory FalseRequirement is fulfilled'
+        );
+
+        $mandatoryOptionalFalseSet = new RequirementSet();
+        $mandatoryOptionalFalseSet->add(new TrueRequirement());
+        $mandatoryOptionalFalseSet->add(new FalseRequirement(array('optional' => true)));
+        $this->assertTrue(
+            $mandatoryOptionalFalseSet->fulfilled(),
+            'A mandatory set of type and with one mandatory True- and one optional FalseRequirement is not fulfilled'
+        );
+
+        $optionalOptionalTrueSet = new RequirementSet(true);
+        $optionalOptionalTrueSet->add(new TrueRequirement(array('optional' => true)));
+        $optionalOptionalTrueSet->add(new FalseRequirement());
+        $this->assertTrue(
+            $optionalOptionalTrueSet->fulfilled(),
+            'A optional set of type and with one optional True- and one mandatory FalseRequirement is not fulfilled'
+        );
+
+        $optionalOptionalFalseSet = new RequirementSet(true);
+        $optionalOptionalFalseSet->add(new TrueRequirement());
+        $optionalOptionalFalseSet->add(new FalseRequirement(array('optional' => true)));
+        $this->assertTrue(
+            $optionalOptionalFalseSet->fulfilled(),
+            'A optional set of type and with one mandatory True- and one optional FalseRequirement is not fulfilled'
+        );
+    }
+
+    public function testFlatMandatoryRequirementsOfTypeOr()
+    {
+        $emptySet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $this->assertFalse($emptySet->fulfilled(), 'A empty mandatory set of type or is fulfilled');
+
+        $singleTrueSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $singleTrueSet->add(new TrueRequirement());
+        $this->assertTrue(
+            $singleTrueSet->fulfilled(),
+            'A mandatory set of type or with a single TrueRequirement is not fulfilled'
+        );
+
+        $singleFalseSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $singleFalseSet->add(new FalseRequirement());
+        $this->assertFalse(
+            $singleFalseSet->fulfilled(),
+            'A mandatory set of type or with a single FalseRequirement is fulfilled'
+        );
+
+        $mixedSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $mixedSet->add(new TrueRequirement());
+        $mixedSet->add(new FalseRequirement());
+        $this->assertTrue(
+            $mixedSet->fulfilled(),
+            'A mandatory set of type or with one True- and one FalseRequirement is not fulfilled'
+        );
+    }
+
+    public function testFlatOptionalRequirementsOfTypeOr()
+    {
+        $emptySet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $this->assertTrue($emptySet->fulfilled(), 'A empty optional set of type or is not fulfilled');
+
+        $singleTrueSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $singleTrueSet->add(new TrueRequirement());
+        $this->assertTrue(
+            $singleTrueSet->fulfilled(),
+            'A optional set of type or with a single TrueRequirement is not fulfilled'
+        );
+
+        $singleFalseSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $singleFalseSet->add(new FalseRequirement());
+        $this->assertTrue(
+            $singleFalseSet->fulfilled(),
+            'A optional set of type or with a single FalseRequirement is not fulfilled'
+        );
+
+        $mixedSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $mixedSet->add(new TrueRequirement());
+        $mixedSet->add(new FalseRequirement());
+        $this->assertTrue(
+            $mixedSet->fulfilled(),
+            'A optional set of type or with one True- and one FalseRequirement is not fulfilled'
+        );
+    }
+
+    public function testFlatMixedRequirementsOfTypeOr()
+    {
+        $mandatoryOptionalTrueSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $mandatoryOptionalTrueSet->add(new TrueRequirement(array('optional' => true)));
+        $mandatoryOptionalTrueSet->add(new FalseRequirement());
+        $this->assertTrue(
+            $mandatoryOptionalTrueSet->fulfilled(),
+            'A mandatory set of type or with one optional True- and one mandatory FalseRequirement is not fulfilled'
+        );
+
+        $mandatoryOptionalFalseSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $mandatoryOptionalFalseSet->add(new TrueRequirement());
+        $mandatoryOptionalFalseSet->add(new FalseRequirement(array('optional' => true)));
+        $this->assertTrue(
+            $mandatoryOptionalFalseSet->fulfilled(),
+            'A mandatory set of type or with one mandatory True- and one optional FalseRequirement is not fulfilled'
+        );
+
+        $optionalOptionalTrueSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $optionalOptionalTrueSet->add(new TrueRequirement(array('optional' => true)));
+        $optionalOptionalTrueSet->add(new FalseRequirement());
+        $this->assertTrue(
+            $optionalOptionalTrueSet->fulfilled(),
+            'A optional set of type or with one optional True- and one mandatory FalseRequirement is not fulfilled'
+        );
+
+        $optionalOptionalFalseSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $optionalOptionalFalseSet->add(new TrueRequirement());
+        $optionalOptionalFalseSet->add(new FalseRequirement(array('optional' => true)));
+        $this->assertTrue(
+            $optionalOptionalFalseSet->fulfilled(),
+            'A optional set of type or with one mandatory True- and one optional FalseRequirement is not fulfilled'
+        );
+    }
+
+    public function testNestedMandatoryRequirementsOfTypeAnd()
+    {
+        $trueSet = new RequirementSet();
+        $trueSet->add(new TrueRequirement());
+        $falseSet = new RequirementSet();
+        $falseSet->add(new FalseRequirement());
+
+        $nestedTrueSet = new RequirementSet();
+        $nestedTrueSet->merge($trueSet);
+        $this->assertTrue(
+            $nestedTrueSet->fulfilled(),
+            'A nested mandatory set of type and with one mandatory TrueRequirement is not fulfilled'
+        );
+
+        $nestedFalseSet = new RequirementSet();
+        $nestedFalseSet->merge($falseSet);
+        $this->assertFalse(
+            $nestedFalseSet->fulfilled(),
+            'A nested mandatory set of type and with one mandatory FalseRequirement is fulfilled'
+        );
+
+        $nestedMixedSet = new RequirementSet();
+        $nestedMixedSet->merge($trueSet);
+        $nestedMixedSet->merge($falseSet);
+        $this->assertFalse(
+            $nestedMixedSet->fulfilled(),
+            'Two nested mandatory sets of type and with one mandatory True- and'
+            . ' one mandatory FalseRequirement respectively are fulfilled'
+        );
+    }
+
+    public function testNestedOptionalRequirementsOfTypeAnd()
+    {
+        $trueSet = new RequirementSet(true);
+        $trueSet->add(new TrueRequirement());
+        $falseSet = new RequirementSet(true);
+        $falseSet->add(new FalseRequirement());
+
+        $nestedTrueSet = new RequirementSet(true);
+        $nestedTrueSet->merge($trueSet);
+        $this->assertTrue(
+            $nestedTrueSet->fulfilled(),
+            'A nested optional set of type and with one mandatory TrueRequirement is not fulfilled'
+        );
+
+        $nestedFalseSet = new RequirementSet(true);
+        $nestedFalseSet->merge($falseSet);
+        $this->assertTrue(
+            $nestedFalseSet->fulfilled(),
+            'A nested optional set of type and with one mandatory FalseRequirement is not fulfilled'
+        );
+
+        $nestedMixedSet = new RequirementSet(true);
+        $nestedMixedSet->merge($trueSet);
+        $nestedMixedSet->merge($falseSet);
+        $this->assertTrue(
+            $nestedMixedSet->fulfilled(),
+            'Two nested optional sets of type and with one mandatory True- and'
+            . ' one mandatory FalseRequirement respectively are not fulfilled'
+        );
+    }
+
+    public function testNestedMixedRequirementsOfTypeAnd()
+    {
+        $mandatoryMandatoryTrueSet = new RequirementSet();
+        $mandatoryMandatoryTrueSet->add(new TrueRequirement());
+        $mandatoryOptionalTrueSet = new RequirementSet();
+        $mandatoryOptionalTrueSet->add(new TrueRequirement(array('optional' => true)));
+        $mandatoryMandatoryFalseSet = new RequirementSet();
+        $mandatoryMandatoryFalseSet->add(new FalseRequirement());
+        $mandatoryOptionalFalseSet = new RequirementSet();
+        $mandatoryOptionalFalseSet->add(new FalseRequirement(array('optional' => true)));
+        $optionalMandatoryTrueSet = new RequirementSet(true);
+        $optionalMandatoryTrueSet->add(new TrueRequirement());
+        $optionalOptionalTrueSet = new RequirementSet(true);
+        $optionalOptionalTrueSet->add(new TrueRequirement(array('optional' => true)));
+        $optionalMandatoryFalseSet = new RequirementSet(true);
+        $optionalMandatoryFalseSet->add(new FalseRequirement());
+        $optionalOptionalFalseSet = new RequirementSet(true);
+        $optionalOptionalFalseSet->add(new FalseRequirement(array('optional' => true)));
+
+        $mandatoryMandatoryOptionalTrueSet = new RequirementSet();
+        $mandatoryMandatoryOptionalTrueSet->merge($mandatoryOptionalTrueSet);
+        $mandatoryMandatoryOptionalTrueSet->merge($mandatoryMandatoryFalseSet);
+        $this->assertFalse(
+            $mandatoryMandatoryOptionalTrueSet->fulfilled(),
+            'A mandatory set of type and with two nested mandatory sets of type and where one has a optional'
+            . ' TrueRequirement and the other one has a mandatory FalseRequirement is fulfilled'
+        );
+
+        $mandatoryMandatoryOptionalFalseSet = new RequirementSet();
+        $mandatoryMandatoryOptionalFalseSet->merge($mandatoryOptionalFalseSet);
+        $mandatoryMandatoryOptionalFalseSet->merge($mandatoryMandatoryTrueSet);
+        $this->assertTrue(
+            $mandatoryMandatoryOptionalFalseSet->fulfilled(),
+            'A mandatory set of type and with two nested mandatory sets of type and where one has a mandatory'
+            . ' TrueRequirement and the other one has a optional FalseRequirement is not fulfilled'
+        );
+
+        $optionalOptionalOptionalTrueSet = new RequirementSet(true);
+        $optionalOptionalOptionalTrueSet->merge($optionalOptionalTrueSet);
+        $optionalOptionalOptionalTrueSet->merge($optionalMandatoryFalseSet);
+        $this->assertTrue(
+            $optionalOptionalOptionalTrueSet->fulfilled(),
+            'A optional set of type and with two nested optional sets of type and where one has a optional'
+            . ' TrueRequirement and the other one has a mandatory FalseRequirement is not fulfilled'
+        );
+
+        $optionalOptionalOptionalFalseSet = new RequirementSet(true);
+        $optionalOptionalOptionalFalseSet->merge($optionalOptionalFalseSet);
+        $optionalOptionalOptionalFalseSet->merge($optionalMandatoryTrueSet);
+        $this->assertTrue(
+            $optionalOptionalOptionalFalseSet->fulfilled(),
+            'A optional set of type and with two nested optional sets of type and where one has a mandatory'
+            . ' TrueRequirement and the other one has a optional FalseRequirement is not fulfilled'
+        );
+    }
+
+    public function testNestedMandatoryRequirementsOfTypeOr()
+    {
+        $trueSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $trueSet->add(new TrueRequirement());
+        $falseSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $falseSet->add(new FalseRequirement());
+
+        $nestedTrueSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $nestedTrueSet->merge($trueSet);
+        $this->assertTrue(
+            $nestedTrueSet->fulfilled(),
+            'A nested mandatory set of type or with one mandatory TrueRequirement is not fulfilled'
+        );
+
+        $nestedFalseSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $nestedFalseSet->merge($falseSet);
+        $this->assertFalse(
+            $nestedFalseSet->fulfilled(),
+            'A nested mandatory set of type or with one mandatory FalseRequirement is fulfilled'
+        );
+
+        $nestedMixedSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $nestedMixedSet->merge($trueSet);
+        $nestedMixedSet->merge($falseSet);
+        $this->assertTrue(
+            $nestedMixedSet->fulfilled(),
+            'Two nested mandatory sets of type or with one mandatory True- and'
+            . ' one mandatory FalseRequirement respectively are not fulfilled'
+        );
+    }
+
+    public function testNestedOptionalRequirementsOfTypeOr()
+    {
+        $trueSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $trueSet->add(new TrueRequirement());
+        $falseSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $falseSet->add(new FalseRequirement());
+
+        $nestedTrueSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $nestedTrueSet->merge($trueSet);
+        $this->assertTrue(
+            $nestedTrueSet->fulfilled(),
+            'A nested optional set of type or with one mandatory TrueRequirement is not fulfilled'
+        );
+
+        $nestedFalseSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $nestedFalseSet->merge($falseSet);
+        $this->assertTrue(
+            $nestedFalseSet->fulfilled(),
+            'A nested optional set of type or with one mandatory FalseRequirement is not fulfilled'
+        );
+
+        $nestedMixedSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $nestedMixedSet->merge($trueSet);
+        $nestedMixedSet->merge($falseSet);
+        $this->assertTrue(
+            $nestedMixedSet->fulfilled(),
+            'Two nested optional sets of type or with one mandatory True- and'
+            . ' one mandatory FalseRequirement respectively are not fulfilled'
+        );
+    }
+
+    public function testNestedMixedRequirementsOfTypeOr()
+    {
+        $mandatoryMandatoryTrueSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $mandatoryMandatoryTrueSet->add(new TrueRequirement());
+        $mandatoryOptionalTrueSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $mandatoryOptionalTrueSet->add(new TrueRequirement(array('optional' => true)));
+        $mandatoryMandatoryFalseSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $mandatoryMandatoryFalseSet->add(new FalseRequirement());
+        $mandatoryOptionalFalseSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $mandatoryOptionalFalseSet->add(new FalseRequirement(array('optional' => true)));
+        $optionalMandatoryTrueSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $optionalMandatoryTrueSet->add(new TrueRequirement());
+        $optionalOptionalTrueSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $optionalOptionalTrueSet->add(new TrueRequirement(array('optional' => true)));
+        $optionalMandatoryFalseSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $optionalMandatoryFalseSet->add(new FalseRequirement());
+        $optionalOptionalFalseSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $optionalOptionalFalseSet->add(new FalseRequirement(array('optional' => true)));
+
+        $mandatoryMandatoryOptionalTrueSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $mandatoryMandatoryOptionalTrueSet->merge($mandatoryOptionalTrueSet);
+        $mandatoryMandatoryOptionalTrueSet->merge($mandatoryMandatoryFalseSet);
+        $this->assertTrue($mandatoryMandatoryOptionalTrueSet->fulfilled());
+
+        $mandatoryMandatoryOptionalFalseSet = new RequirementSet(false, RequirementSet::MODE_OR);
+        $mandatoryMandatoryOptionalFalseSet->merge($mandatoryOptionalFalseSet);
+        $mandatoryMandatoryOptionalFalseSet->merge($mandatoryMandatoryTrueSet);
+        $this->assertTrue($mandatoryMandatoryOptionalFalseSet->fulfilled());
+
+        $optionalOptionalOptionalTrueSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $optionalOptionalOptionalTrueSet->merge($optionalOptionalTrueSet);
+        $optionalOptionalOptionalTrueSet->merge($optionalMandatoryFalseSet);
+        $this->assertTrue($optionalOptionalOptionalTrueSet->fulfilled());
+
+        $optionalOptionalOptionalFalseSet = new RequirementSet(true, RequirementSet::MODE_OR);
+        $optionalOptionalOptionalFalseSet->merge($optionalOptionalFalseSet);
+        $optionalOptionalOptionalFalseSet->merge($optionalMandatoryTrueSet);
+        $this->assertTrue($optionalOptionalOptionalFalseSet->fulfilled());
+    }
+
+    public function testNestedMandatoryRequirementsOfDifferentTypes()
+    {
+        $true = new TrueRequirement();
+        $false = new FalseRequirement();
+
+        $level1And = new RequirementSet();
+        $level2FirstOr = new RequirementSet(false, RequirementSet::MODE_OR);
+        $level2SecondOr = new RequirementSet(false, RequirementSet::MODE_OR);
+        $level1And->merge($level2FirstOr)->merge($level2SecondOr);
+        $level3FirstAnd = new RequirementSet();
+        $level3SecondAnd = new RequirementSet();
+        $level2FirstOr->merge($level3FirstAnd)->merge($level3SecondAnd);
+        $level2SecondOr->merge($level3FirstAnd)->merge($level3SecondAnd);
+        $level3FirstAnd->add($true)->add($true);
+        $level3SecondAnd->add($false)->add($true);
+        $this->assertTrue($level1And->fulfilled());
+
+        $level1Or = new RequirementSet(false, RequirementSet::MODE_OR);
+        $level2FirstAnd = new RequirementSet();
+        $level2SecondAnd = new RequirementSet();
+        $level1Or->merge($level2FirstAnd)->merge($level2SecondAnd);
+        $level3FirstOr = new RequirementSet(false, RequirementSet::MODE_OR);
+        $level3SecondOr = new RequirementSet(false, RequirementSet::MODE_OR);
+        $level2FirstAnd->merge($level3FirstOr)->merge($level3SecondOr);
+        $level2SecondAnd->merge($level3FirstOr)->merge($level3SecondOr);
+        $level3FirstOr->add($false);
+        $level3SecondOr->add($true);
+        $this->assertFalse($level1Or->fulfilled());
+    }
+
+    public function testNestedOptionalRequirementsOfDifferentTypes()
+    {
+        $true = new TrueRequirement();
+        $false = new FalseRequirement();
+
+        $level1And = new RequirementSet();
+        $level2FirstAnd = new RequirementSet(true);
+        $level2SecondAnd = new RequirementSet(true);
+        $level1And->merge($level2FirstAnd)->merge($level2SecondAnd);
+        $level3FirstOr = new RequirementSet(true, RequirementSet::MODE_OR);
+        $level3SecondOr = new RequirementSet(true, RequirementSet::MODE_OR);
+        $level2FirstAnd->merge($level3FirstOr)->merge($level3SecondOr);
+        $level2SecondAnd->merge($level3FirstOr)->merge($level3SecondOr);
+        $level3FirstOr->add($false);
+        $level3SecondOr->add($false);
+        $this->assertFalse($level1And->fulfilled());
+        $this->assertTrue($level2FirstAnd->fulfilled());
+        $this->assertTrue($level2SecondAnd->fulfilled());
+
+        $level1Or = new RequirementSet(false, RequirementSet::MODE_OR);
+        $level2FirstOr = new RequirementSet(true, RequirementSet::MODE_OR);
+        $level2SecondOr = new RequirementSet(true, RequirementSet::MODE_OR);
+        $level1Or->merge($level2FirstOr)->merge($level2SecondOr);
+        $level3FirstAnd = new RequirementSet(true);
+        $level3SecondAnd = new RequirementSet(true);
+        $level2FirstOr->merge($level3FirstAnd)->merge($level3SecondAnd);
+        $level2SecondOr->merge($level3FirstAnd)->merge($level3SecondAnd);
+        $level3FirstAnd->add($true)->add($true);
+        $level3SecondAnd->add($false)->add($true);
+        $this->assertTrue($level1Or->fulfilled());
+    }
+
+    public function testNestedMixedRequirementsOfDifferentTypes()
+    {
+        $this->markTestIncomplete();
+    }
+}