diff --git a/mailpoet/tests/unit/Automation/Engine/Validation/WorkflowRules/UnknownStepRuleTest.php b/mailpoet/tests/unit/Automation/Engine/Validation/WorkflowRules/UnknownStepRuleTest.php
new file mode 100644
index 0000000000..7f1a07ac3d
--- /dev/null
+++ b/mailpoet/tests/unit/Automation/Engine/Validation/WorkflowRules/UnknownStepRuleTest.php
@@ -0,0 +1,106 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\Validation\WorkflowRules;
+
+require_once __DIR__ . '/WorkflowRuleTest.php';
+
+use MailPoet\Automation\Engine\Control\RootStep;
+use MailPoet\Automation\Engine\Data\Step;
+use MailPoet\Automation\Engine\Data\Workflow;
+use MailPoet\Automation\Engine\Exceptions\UnexpectedValueException;
+use MailPoet\Automation\Engine\Registry;
+use MailPoet\Automation\Engine\Storage\WorkflowStorage;
+use MailPoet\Automation\Engine\Validation\WorkflowGraph\WorkflowWalker;
+
+class UnknownStepRuleTest extends WorkflowRuleTest {
+  public function testItDetectsModificationWithoutExistingWorkflow(): void {
+    $workflow = $this->getWorkflow();
+    $this->expectException(UnexpectedValueException::class);
+    $this->expectExceptionMessage("Modification of step 'core:root' of type 'root' with ID 'root' is not supported when the related plugin is not active.");
+    (new WorkflowWalker())->walk($workflow, [$this->getRule()]);
+  }
+
+  public function testItDetectsAddedStep(): void {
+    $workflow = $this->getWorkflow();
+    $existingWorkflow = $this->make(Workflow::class, [
+      'getId' => 1,
+      'getSteps' => [],
+    ]);
+
+    $this->expectException(UnexpectedValueException::class);
+    $this->expectExceptionMessage("Modification of step 'core:root' of type 'root' with ID 'root' is not supported when the related plugin is not active.");
+    (new WorkflowWalker())->walk($workflow, [$this->getRule($existingWorkflow)]);
+  }
+
+  public function testItDetectsChangedStep(): void {
+    $workflow = $this->getWorkflow();
+    $existingWorkflow = $this->make(Workflow::class, [
+      'getId' => 1,
+      'getSteps' => [
+        'root' => $this->createStep('root', Step::TYPE_ROOT, ['next-step-id']),
+      ],
+    ]);
+
+    $this->expectException(UnexpectedValueException::class);
+    $this->expectExceptionMessage("Modification of step 'core:root' of type 'root' with ID 'root' is not supported when the related plugin is not active.");
+    (new WorkflowWalker())->walk($workflow, [$this->getRule($existingWorkflow)]);
+  }
+
+
+  public function testItPassesWithDeletedStep(): void {
+    $workflow = $this->getWorkflow();
+    $existingWorkflow = $this->make(Workflow::class, [
+      'getId' => 1,
+      'getSteps' => [
+        'root' => new Step('root', 'root', 'core:root', [], []),
+        'abc' => $this->createStep('abc', Step::TYPE_TRIGGER, []),
+      ],
+    ]);
+    (new WorkflowWalker())->walk($workflow, [$this->getRule($existingWorkflow)]);
+  }
+
+  public function testItPassesWithoutChanges(): void {
+    $workflow = $this->getWorkflow();
+    (new WorkflowWalker())->walk($workflow, [$this->getRule($workflow)]);
+  }
+
+  public function testItPassesWithExistingRegistryStep(): void {
+    $workflow = $this->make(Workflow::class, [
+      'getId' => 1,
+      'getSteps' => [
+        'root' => new Step('root', 'root', 'core:root', [], []),
+      ],
+    ]);
+
+    $existingWorkflow = $this->make(Workflow::class, [
+      'getId' => 1,
+      'getSteps' => [
+        'root' => new Step('root', 'root', 'core:root', ['key' => 'value'], []),
+      ],
+    ]);
+    (new WorkflowWalker())->walk($workflow, [$this->getRule($existingWorkflow, [new RootStep()])]);
+  }
+
+  private function getRule(Workflow $existingWorkflow = null, array $steps = []): UnknownStepRule {
+    $stepMap = [];
+    foreach ($steps as $step) {
+      $stepMap[$step->getKey()] = $step;
+    }
+    $registry = $this->make(Registry::class, [
+      'steps' => $stepMap,
+    ]);
+    $storage = $this->make(WorkflowStorage::class, [
+      'getWorkflow' => $existingWorkflow,
+    ]);
+    return new UnknownStepRule($registry, $storage);
+  }
+
+  private function getWorkflow(): Workflow {
+    return $this->make(Workflow::class, [
+      'getId' => 1,
+      'getSteps' => [
+        'root' => new Step('root', 'root', 'core:root', [], []),
+      ],
+    ]);
+  }
+}
diff --git a/mailpoet/tests/unit/Automation/Engine/Validation/WorkflowRules/ValidStepArgsRuleTest.php b/mailpoet/tests/unit/Automation/Engine/Validation/WorkflowRules/ValidStepArgsRuleTest.php
new file mode 100644
index 0000000000..58687e001c
--- /dev/null
+++ b/mailpoet/tests/unit/Automation/Engine/Validation/WorkflowRules/ValidStepArgsRuleTest.php
@@ -0,0 +1,48 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\Validation\WorkflowRules;
+
+require_once __DIR__ . '/WorkflowRuleTest.php';
+
+use Codeception\Stub\Expected;
+use MailPoet\Automation\Engine\Control\RootStep;
+use MailPoet\Automation\Engine\Data\Step;
+use MailPoet\Automation\Engine\Data\Workflow;
+use MailPoet\Automation\Engine\Registry;
+use MailPoet\Automation\Engine\Validation\WorkflowGraph\WorkflowWalker;
+use MailPoet\Validator\Validator;
+
+class ValidStepArgsRuleTest extends WorkflowRuleTest {
+  public function testItRunsArgsValidation(): void {
+    $registry = $this->make(Registry::class, [
+      'steps' => ['core:root' => new RootStep()],
+    ]);
+
+    $validator = $this->make(Validator::class, [
+      'validate' => Expected::once(),
+    ]);
+
+    $rule = new ValidStepArgsRule($registry, $validator);
+    $workflow = $this->getWorkflow();
+    (new WorkflowWalker())->walk($workflow, [$rule]);
+  }
+
+  public function testItSkipsArgsValidationForNonExistentStep(): void {
+    $registry = $this->make(Registry::class);
+    $validator = $this->make(Validator::class, [
+      'validate' => Expected::never(),
+    ]);
+
+    $rule = new ValidStepArgsRule($registry, $validator);
+    $workflow = $this->getWorkflow();
+    (new WorkflowWalker())->walk($workflow, [$rule]);
+  }
+
+  private function getWorkflow(): Workflow {
+    return $this->make(Workflow::class, [
+      'getSteps' => [
+        'root' => new Step('root', 'root', 'core:root', [], []),
+      ],
+    ]);
+  }
+}