diff --git a/packages/ckeditor5-mermaid/tests/commands/insertMermaidCommand.ts b/packages/ckeditor5-mermaid/tests/commands/insertMermaidCommand.ts
index d65ba11f1..7f7e5e741 100644
--- a/packages/ckeditor5-mermaid/tests/commands/insertMermaidCommand.ts
+++ b/packages/ckeditor5-mermaid/tests/commands/insertMermaidCommand.ts
@@ -1,4 +1,8 @@
 import { ClassicEditor, Paragraph, _setModelData as setModelData, _getModelData as getModelData } from 'ckeditor5';
+import { afterEach, beforeEach, describe, it } from 'vitest';
+import MermaidEditing from '../../dist/mermaidediting';
+import InsertMermaidCommand from '../../dist/commands/insertMermaidCommand';
+import { expect } from 'vitest';
 
 /* global document */
 
diff --git a/packages/ckeditor5-mermaid/tests/commands/mermaidPreviewCommand.ts b/packages/ckeditor5-mermaid/tests/commands/mermaidPreviewCommand.ts
index b1f94fa80..ff47dd936 100644
--- a/packages/ckeditor5-mermaid/tests/commands/mermaidPreviewCommand.ts
+++ b/packages/ckeditor5-mermaid/tests/commands/mermaidPreviewCommand.ts
@@ -2,6 +2,8 @@ import { ClassicEditor, Paragraph, _setModelData as setModelData, _getModelData
 
 import MermaidPreviewCommand from '../../src/commands/mermaidPreviewCommand.js';
 import MermaidEditing from '../../src/mermaidediting.js';
+import { afterEach, beforeEach, describe, it } from 'vitest';
+import { expect } from 'vitest';
 
 /* global document */
 
diff --git a/packages/ckeditor5-mermaid/tests/commands/mermaidSourceViewCommand.ts b/packages/ckeditor5-mermaid/tests/commands/mermaidSourceViewCommand.ts
index 94675bf8e..6836b6eec 100644
--- a/packages/ckeditor5-mermaid/tests/commands/mermaidSourceViewCommand.ts
+++ b/packages/ckeditor5-mermaid/tests/commands/mermaidSourceViewCommand.ts
@@ -2,6 +2,8 @@ import { ClassicEditor, Paragraph, _setModelData as setModelData, _getModelData
 
 import MermaidSourceViewCommand from '../../src/commands/mermaidSourceViewCommand.js';
 import MermaidEditing from '../../src/mermaidediting.js';
+import { afterEach, beforeEach, describe, it } from 'vitest';
+import { expect } from 'vitest';
 
 /* global document */
 
diff --git a/packages/ckeditor5-mermaid/tests/commands/mermaidSplitViewCommand.ts b/packages/ckeditor5-mermaid/tests/commands/mermaidSplitViewCommand.ts
index 680197d98..c9d280e38 100644
--- a/packages/ckeditor5-mermaid/tests/commands/mermaidSplitViewCommand.ts
+++ b/packages/ckeditor5-mermaid/tests/commands/mermaidSplitViewCommand.ts
@@ -2,6 +2,8 @@ import { ClassicEditor, Paragraph, _setModelData as setModelData, _getModelData
 
 import MermaidSplitViewCommand from '../../src/commands/mermaidSplitViewCommand.js';
 import MermaidEditing from '../../src/mermaidediting.js';
+import { afterEach, beforeEach, describe, it } from 'vitest';
+import { expect } from 'vitest';
 
 /* global document */
 
diff --git a/packages/ckeditor5-mermaid/tests/index.ts b/packages/ckeditor5-mermaid/tests/index.ts
index b234b0905..06f8e2d83 100644
--- a/packages/ckeditor5-mermaid/tests/index.ts
+++ b/packages/ckeditor5-mermaid/tests/index.ts
@@ -6,6 +6,8 @@ import insertMermaidIcon from './../theme/icons/insert.svg';
 import previewModeIcon from './../theme/icons/preview-mode.svg';
 import splitModeIcon from './../theme/icons/split-mode.svg';
 import sourceModeIcon from './../theme/icons/source-mode.svg';
+import { describe, it } from 'vitest';
+import { expect } from 'vitest';
 
 describe( 'CKEditor5 Mermaid DLL', () => {
 	it( 'exports MermaidWidget', () => {
diff --git a/packages/ckeditor5-mermaid/tests/manual/mermaid.ts b/packages/ckeditor5-mermaid/tests/manual/mermaid.ts
index 7d5190088..c1c6ebcef 100644
--- a/packages/ckeditor5-mermaid/tests/manual/mermaid.ts
+++ b/packages/ckeditor5-mermaid/tests/manual/mermaid.ts
@@ -5,7 +5,7 @@
 
 /* globals console, window, document */
 
-import { ClassicEditor, Typing, Paragraph, Undo, Enter, Clipboard, Link, Bold, Italic, CodeBlock } from '@ckeditor/ckeditor5-editor-classic';
+import { ClassicEditor, Typing, Paragraph, Undo, Enter, Clipboard, Link, Bold, Italic, CodeBlock } from 'ckeditor5';
 
 import Mermaid from '../../src/mermaid.js';
 
diff --git a/packages/ckeditor5-mermaid/tests/mermaid.ts b/packages/ckeditor5-mermaid/tests/mermaid.ts
index 1ae7abd8a..88638d033 100644
--- a/packages/ckeditor5-mermaid/tests/mermaid.ts
+++ b/packages/ckeditor5-mermaid/tests/mermaid.ts
@@ -1,6 +1,8 @@
 import { ClassicEditor, Essentials, Paragraph, Heading, _setModelData as setModelData } from 'ckeditor5';
 
 import Mermaid from '../src/mermaid.js';
+import { afterEach, beforeEach, describe, it } from 'vitest';
+import { expect } from 'vitest';
 
 /* global document */
 
diff --git a/packages/ckeditor5-mermaid/tests/mermaidediting.ts b/packages/ckeditor5-mermaid/tests/mermaidediting.ts
index 16b6bf257..29384ee5f 100644
--- a/packages/ckeditor5-mermaid/tests/mermaidediting.ts
+++ b/packages/ckeditor5-mermaid/tests/mermaidediting.ts
@@ -1,5 +1,8 @@
 import { ClassicEditor, Essentials, Paragraph, Heading, CodeBlockEditing, _setModelData as setModelData, _getModelData as getModelData, _getViewData as getViewData } from 'ckeditor5';
 import MermaidEditing from '../src/mermaidediting.js';
+import { afterEach, beforeEach, describe, it } from 'vitest';
+import { expect } from 'vitest';
+import { vi } from 'vitest';
 
 /* global document */
 
@@ -240,7 +243,7 @@ describe( 'MermaidEditing', () => {
 						} );
 
 						expect( renderMermaidStub.callCount ).to.equal( 1 );
-						sinon.assert.calledWithExactly( renderMermaidStub, domPreviewContainer );
+						expect(renderMermaidStub).toBeCalledWith(domPreviewContainer);
 					} );
 				} );
 			} );
diff --git a/packages/ckeditor5-mermaid/tests/mermaidtoolbar.ts b/packages/ckeditor5-mermaid/tests/mermaidtoolbar.ts
index 948a47a41..fe0eb58cc 100644
--- a/packages/ckeditor5-mermaid/tests/mermaidtoolbar.ts
+++ b/packages/ckeditor5-mermaid/tests/mermaidtoolbar.ts
@@ -1,6 +1,8 @@
 import { ClassicEditor as ClassicTestEditor, Essentials, Paragraph, WidgetToolbarRepository, _setModelData as setData } from 'ckeditor5';
 
 import Mermaid from '../src/mermaid.js';
+import { afterEach, beforeEach, describe, it } from 'vitest';
+import { expect } from 'vitest';
 
 /* global document */
 
diff --git a/packages/ckeditor5-mermaid/tests/mermaidui.ts b/packages/ckeditor5-mermaid/tests/mermaidui.ts
index 698293c1f..d5fc8bf1b 100644
--- a/packages/ckeditor5-mermaid/tests/mermaidui.ts
+++ b/packages/ckeditor5-mermaid/tests/mermaidui.ts
@@ -2,6 +2,8 @@ import { ClassicEditor, _setModelData as setModelData } from 'ckeditor5';
 
 import Mermaid from '../src/mermaid.js';
 import MermaidUI from '../src/mermaidui.js';
+import { afterEach, beforeEach, describe, it } from 'vitest';
+import { expect } from 'vitest';
 
 /* global document */