ci(e2e): Only run changed E2E tests (#17077)

This pr changes the detection logic for the e2e tests directory.

Before we always ran every test whenever something changed in this dir.
With this change we check for changed files in the test apps and only
run all tests if shared code has been changed.

Author: chargome

dev-packages/e2e-tests/lib/getTestMatrix.ts

@@ -143,8 +143,27 @@ function getAffectedTestApplications(
     .map(line => line.trim())
     .filter(Boolean);
 
-  // If something in e2e tests themselves are changed, just run everything
+  // If something in e2e tests themselves are changed, check if only test applications were changed
   if (affectedProjects.includes('@sentry-internal/e2e-tests')) {
+    try {
+      const changedTestApps = getChangedTestApps(base, head);
+
+      // Shared code was changed, run all tests
+      if (changedTestApps === false) {
+        return testApplications;
+      }
+
+      // Only test applications that were changed, run selectively
+      if (changedTestApps.size > 0) {
+        return testApplications.filter(testApp => changedTestApps.has(testApp));
+      }
+    } catch (error) {
+      // eslint-disable-next-line no-console
+      console.error('Failed to get changed files, running all tests:', error);
+      return testApplications;
+    }
+
+    // Fall back to running all tests
     return testApplications;
   }
 
@@ -153,3 +172,32 @@ function getAffectedTestApplications(
     return sentryDependencies.some(dep => affectedProjects.includes(dep));
   });
 }
+
+function getChangedTestApps(base: string, head?: string): false | Set<string> {
+  const changedFiles = execSync(`git diff --name-only ${base}${head ? `..${head}` : ''} -- dev-packages/e2e-tests/`, {
+    encoding: 'utf-8',
+  })
+    .toString()
+    .split('\n')
+    .map(line => line.trim())
+    .filter(Boolean);
+
+  const changedTestApps: Set<string> = new Set();
+  const testAppsPrefix = 'dev-packages/e2e-tests/test-applications/';
+
+  for (const file of changedFiles) {
+    if (!file.startsWith(testAppsPrefix)) {
+      // Shared code change - need to run all tests
+      return false;
+    }
+
+    const pathAfterPrefix = file.slice(testAppsPrefix.length);
+    const slashIndex = pathAfterPrefix.indexOf('/');
+
+    if (slashIndex > 0) {
+      changedTestApps.add(pathAfterPrefix.slice(0, slashIndex));
+    }
+  }
+
+  return changedTestApps;
+}