CLI: Skip a11y addon automigration prompting when not applicable

code/lib/cli-storybook/src/automigrate/fixes/addon-a11y-addon-test.test.ts

@@ -159,7 +159,7 @@ describe('addonA11yAddonTest', () => {
       });
     });
 
-    it.skip('should return previewFile and transformedPreviewCode if preview file exists', async () => {
+    it('should return previewFile and transformedPreviewCode if preview file exists', async () => {
       vi.mocked(getAddonNames).mockReturnValue([
         '@storybook/addon-a11y',
         '@storybook/addon-vitest',
@@ -191,8 +191,45 @@ describe('addonA11yAddonTest', () => {
         transformedPreviewCode: expect.any(String),
         transformedSetupCode: null,
         skipPreviewTransformation: false,
-        skipVitestSetupTransformation: false,
+        skipVitestSetupTransformation: true,
+      });
+    });
+
+    it('should return null if vitest.setup file does not exist and preview file has the necessary transformations', async () => {
+      vi.mocked(getAddonNames).mockReturnValue([
+        '@storybook/addon-a11y',
+        '@storybook/addon-vitest',
+      ]);
+      vi.mocked(existsSync).mockImplementation((p) => {
+        if (p.toString().includes('preview')) {
+          return true;
+        } else {
+          return false;
+        }
+      });
+      vi.mocked(readFileSync).mockImplementation((p) => {
+        if (p.toString().includes('preview')) {
+          return `
+            export default {
+              parameters: {
+                a11y: {
+                  test: 'todo'
+                }
+              }
+            }
+          `;
+        } else {
+          return '';
+        }
       });
+
+      const result = await addonA11yAddonTest.check({
+        mainConfig: {
+          framework: '@storybook/react-vite',
+        },
+        configDir,
+      } as any);
+      expect(result).toBeNull();
     });
 
     it('should return setupFile and null transformedSetupCode if transformation fails', async () => {
@@ -265,7 +302,7 @@ describe('addonA11yAddonTest', () => {
         transformedPreviewCode: null,
         transformedSetupCode: null,
         skipPreviewTransformation: false,
-        skipVitestSetupTransformation: false,
+        skipVitestSetupTransformation: true,
       });
     });
 

code/lib/cli-storybook/src/automigrate/fixes/addon-a11y-addon-test.ts

@@ -72,21 +72,33 @@ export const addonA11yAddonTest: Fix<AddonA11yAddonTestOptions> = {
         .map((ext) => path.join(configDir, `preview${ext}`))
         .find((filePath) => existsSync(filePath)) ?? null;
 
-    let skipVitestSetupTransformation = hasCsfFactoryPreview;
+    // Without a setup file there is nothing to transform: since Storybook 10.3
+    // the vitest plugin auto-provisions preview annotations (including addon-a11y's).
+    let skipVitestSetupTransformation = hasCsfFactoryPreview || !vitestSetupFile;
     let skipPreviewTransformation = false;
 
-    if (vitestSetupFile && previewFile) {
-      const vitestSetupSource = readFileSync(vitestSetupFile, 'utf8');
-      const previewSetupSource = readFileSync(previewFile, 'utf8');
-
-      skipVitestSetupTransformation ||= vitestSetupSource.includes('@storybook/addon-a11y');
-      skipPreviewTransformation ||= !shouldPreviewFileBeTransformed(previewSetupSource);
+    if (vitestSetupFile && !skipVitestSetupTransformation) {
+      try {
+        const vitestSetupSource = readFileSync(vitestSetupFile, 'utf8');
+        skipVitestSetupTransformation = vitestSetupSource.includes('@storybook/addon-a11y');
+      } catch {
+        // leave the flag as-is; getTransformedSetupCode handles unreadable files
+      }
+    }
 
-      if (skipVitestSetupTransformation && skipPreviewTransformation) {
-        return null;
+    if (previewFile) {
+      try {
+        const previewSetupSource = readFileSync(previewFile, 'utf8');
+        skipPreviewTransformation = !shouldPreviewFileBeTransformed(previewSetupSource);
+      } catch {
+        // leave the flag as-is; getTransformedPreviewCode handles unreadable files
       }
     }
 
+    if (skipVitestSetupTransformation && skipPreviewTransformation) {
+      return null;
+    }
+
     const getTransformedSetupCode = () => {
       if (!vitestSetupFile || skipVitestSetupTransformation) {
         return null;
@@ -95,7 +107,7 @@ export const addonA11yAddonTest: Fix<AddonA11yAddonTestOptions> = {
       try {
         const vitestSetupSource = readFileSync(vitestSetupFile, 'utf8');
         return transformSetupFile(vitestSetupSource);
-      } catch (e) {
+      } catch {
         return null;
       }
     };
@@ -108,7 +120,7 @@ export const addonA11yAddonTest: Fix<AddonA11yAddonTestOptions> = {
       try {
         const previewSetupSource = readFileSync(previewFile, 'utf8');
         return transformPreviewFile(previewSetupSource, previewFile);
-      } catch (e) {
+      } catch {
         return null;
       }
     };