only in patch2:
unchanged:
--- a/core/modules/workflows/tests/src/Unit/WorkflowTest.php
+++ b/core/modules/workflows/tests/src/Unit/WorkflowTest.php
@@ -611,6 +611,73 @@ public function testSetTransitionFromStatesMissingState() {
   }
 
   /**
+   * @covers ::setTransitionToState
+   */
+  public function testSetTransitionToState() {
+    $workflow = new Workflow(['id' => 'test', 'type' => 'test_type'], 'workflow');
+    $workflow
+      ->addState('draft', 'Draft')
+      ->addState('published', 'Published')
+      ->addState('archived', 'Archived')
+      ->addTransition('test', 'Test', ['draft'], 'draft');
+
+    $this->assertFalse($workflow->hasTransitionFromStateToState('draft', 'published'));
+    $this->assertTrue($workflow->hasTransitionFromStateToState('draft', 'draft'));
+    $this->assertFalse($workflow->hasTransitionFromStateToState('published', 'draft'));
+    $this->assertFalse($workflow->hasTransitionFromStateToState('archived', 'draft'));
+    $workflow->setTransitionToState('test', 'published');
+    $this->assertTrue($workflow->hasTransitionFromStateToState('draft', 'published'));
+    $this->assertFalse($workflow->hasTransitionFromStateToState('draft', 'draft'));
+    $this->assertFalse($workflow->hasTransitionFromStateToState('published', 'draft'));
+    $this->assertFalse($workflow->hasTransitionFromStateToState('archived', 'draft'));
+  }
+
+  /**
+   * @covers ::setTransitionToState
+   */
+  public function testSetTransitionToStateMissingTransition() {
+    $this->setExpectedException(\InvalidArgumentException::class, "The transition 'test' does not exist in workflow 'test'");
+    $workflow = new Workflow(['id' => 'test', 'type' => 'test_type'], 'workflow');
+    $workflow
+      ->addState('draft', 'Draft')
+      ->addState('published', 'Published')
+      ->addState('archived', 'Archived')
+      ->addTransition('create_new_draft', 'Create new draft', ['draft'], 'draft');
+
+    $workflow->setTransitionToState('test', 'published');
+  }
+
+  /**
+   * @covers ::setTransitionToState
+   */
+  public function testSetTransitionToStateMissingState() {
+    $this->setExpectedException(\InvalidArgumentException::class, "The state 'published' does not exist in workflow 'test'");
+    $workflow = new Workflow(['id' => 'test', 'type' => 'test_type'], 'workflow');
+    $workflow
+      ->addState('draft', 'Draft')
+      ->addState('archived', 'Archived')
+      ->addTransition('create_new_draft', 'Create new draft', ['draft'], 'draft');
+
+    $workflow->setTransitionToState('create_new_draft', 'published');
+  }
+
+  /**
+   * @covers ::setTransitionToState
+   */
+  public function testSetTransitionToStateAlreadyExists() {
+    $this->setExpectedException(\InvalidArgumentException::class, "The 'create_new_draft' transition already allows 'draft' to 'draft' transitions in workflow 'test'");
+    $workflow = new Workflow(['id' => 'test', 'type' => 'test_type'], 'workflow');
+    $workflow
+      ->addState('draft', 'Draft')
+      ->addState('archived', 'Archived')
+      ->addState('needs_review', 'Needs Review')
+      ->addTransition('create_new_draft', 'Create new draft', ['draft'], 'draft')
+      ->addTransition('needs_review', 'Needs review', ['draft'], 'needs_review');
+
+    $workflow->setTransitionToState('needs_review', 'draft');
+  }
+
+  /**
    * @covers ::deleteTransition
    */
   public function testDeleteTransition() {