Write robust assertions

When writing tests, ensure assertions can handle non-deterministic content while providing clear failure context:

1. For non-deterministic content (like absolute paths in error outputs):
   • Use targeted assertions (toContain(), toInclude()) instead of full snapshots
   • Add explanatory comments about why standard approaches aren’t being used

   // GOOD
   // rspack returns error content that contains absolute paths which are non deterministic
   await session.assertHasRedbox();
   expect(redboxContent).toContain("Module not found: Can't resolve 'dns'");
   expect(redboxLabel).toContain('Build Error');
      
   // AVOID
   await expect(browser).toDisplayRedbox(`
     "error": {
       "message": "[absolute path that will change]",
     }
   `);
   

2. For DOM testing:
   • Use specialized tools like cheerio instead of string manipulation
   • Add identifiers to tested elements to make assertions more reliable

   // GOOD
   const $ = await next.render$('/');
   expect($('#server-value').text()).toBe('Server value: foobar');
      
   // AVOID
   const html = (await res.text()).replaceAll(/<!-- -->/g, '');
   expect(html).toContain('Server value: foobar');
   

3. For diagnostic tests:
   • Include contextual information (e.g., filenames) in assertions
   • Use declarative assertion patterns over iterative approaches

   // GOOD
   expect(diagnosedFiles).toEqual({
     'page.tsx': { code: NEXT_TS_ERRORS.INVALID_METADATA_EXPORT, /*...*/ },
     'layout.tsx': { code: NEXT_TS_ERRORS.INVALID_METADATA_EXPORT, /*...*/ }
   });
      
   // AVOID
   for (const tsFile of tsFiles) {
     const diagnostics = languageService.getSemanticDiagnostics(tsFile);
     expect(diagnostics.length).toBe(1);
     // No context about which file failed if assertion fails
   }