diff --git a/packages/ckeditor5-mermaid/tests/commands/insertMermaidCommand.js b/packages/ckeditor5-mermaid/tests/commands/insertMermaidCommand.ts
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rename from packages/ckeditor5-mermaid/tests/commands/insertMermaidCommand.js
rename to packages/ckeditor5-mermaid/tests/commands/insertMermaidCommand.ts
diff --git a/packages/ckeditor5-mermaid/tests/commands/mermaidPreviewCommand.js b/packages/ckeditor5-mermaid/tests/commands/mermaidPreviewCommand.ts
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rename from packages/ckeditor5-mermaid/tests/commands/mermaidPreviewCommand.js
rename to packages/ckeditor5-mermaid/tests/commands/mermaidPreviewCommand.ts
diff --git a/packages/ckeditor5-mermaid/tests/commands/mermaidSourceViewCommand.js b/packages/ckeditor5-mermaid/tests/commands/mermaidSourceViewCommand.ts
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rename from packages/ckeditor5-mermaid/tests/commands/mermaidSourceViewCommand.js
rename to packages/ckeditor5-mermaid/tests/commands/mermaidSourceViewCommand.ts
diff --git a/packages/ckeditor5-mermaid/tests/commands/mermaidSplitViewCommand.js b/packages/ckeditor5-mermaid/tests/commands/mermaidSplitViewCommand.ts
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rename from packages/ckeditor5-mermaid/tests/commands/mermaidSplitViewCommand.js
rename to packages/ckeditor5-mermaid/tests/commands/mermaidSplitViewCommand.ts
diff --git a/packages/ckeditor5-mermaid/tests/index.js b/packages/ckeditor5-mermaid/tests/index.ts
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rename from packages/ckeditor5-mermaid/tests/index.js
rename to packages/ckeditor5-mermaid/tests/index.ts
diff --git a/packages/ckeditor5-mermaid/tests/manual/markdown.js b/packages/ckeditor5-mermaid/tests/manual/markdown.ts
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rename from packages/ckeditor5-mermaid/tests/manual/markdown.js
rename to packages/ckeditor5-mermaid/tests/manual/markdown.ts
diff --git a/packages/ckeditor5-mermaid/tests/manual/mermaid.js b/packages/ckeditor5-mermaid/tests/manual/mermaid.ts
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rename from packages/ckeditor5-mermaid/tests/manual/mermaid.js
rename to packages/ckeditor5-mermaid/tests/manual/mermaid.ts
diff --git a/packages/ckeditor5-mermaid/tests/mermaid.js b/packages/ckeditor5-mermaid/tests/mermaid.ts
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rename from packages/ckeditor5-mermaid/tests/mermaid.js
rename to packages/ckeditor5-mermaid/tests/mermaid.ts
diff --git a/packages/ckeditor5-mermaid/tests/mermaidediting.js b/packages/ckeditor5-mermaid/tests/mermaidediting.ts
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rename from packages/ckeditor5-mermaid/tests/mermaidediting.js
rename to packages/ckeditor5-mermaid/tests/mermaidediting.ts
diff --git a/packages/ckeditor5-mermaid/tests/mermaidtoolbar.js b/packages/ckeditor5-mermaid/tests/mermaidtoolbar.ts
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rename from packages/ckeditor5-mermaid/tests/mermaidtoolbar.js
rename to packages/ckeditor5-mermaid/tests/mermaidtoolbar.ts
diff --git a/packages/ckeditor5-mermaid/tests/mermaidui.js b/packages/ckeditor5-mermaid/tests/mermaidui.ts
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rename from packages/ckeditor5-mermaid/tests/mermaidui.js
rename to packages/ckeditor5-mermaid/tests/mermaidui.ts