test(android): Wait for the previous session move in InternalSentrySdkTest (#6358)

Sentry.init moves session.json to previous_session.json on the executor. When that task ran after a test persisted the live session, the test could no longer read session.json, and PreviousSessionFinalizer sent the moved session as an extra envelope. Wait for the move in the fixture and re-enable the test that was ignored for the same flake.

Co-authored-by: sentry-junior[bot] <264270552+sentry-junior[bot]@users.noreply.github.com>
Co-authored-by: Nelson Osacky <nelson.osacky@sentry.io>

Author: sentry-junior[bot]

sentry-android-core/src/test/java/io/sentry/android/core/InternalSentrySdkTest.kt

@@ -38,13 +38,13 @@ import java.io.ByteArrayOutputStream
 import java.io.InputStreamReader
 import java.util.concurrent.atomic.AtomicReference
 import kotlin.test.BeforeTest
-import kotlin.test.Ignore
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertNotEquals
 import kotlin.test.assertNotNull
 import kotlin.test.assertNull
 import kotlin.test.assertTrue
+import org.awaitility.kotlin.await
 import org.junit.runner.RunWith
 import org.mockito.kotlin.mock
 import org.mockito.kotlin.whenever
@@ -87,6 +87,12 @@ class InternalSentrySdkTest {
         }
       }
 
+      // Sentry.init moves any leftover session.json to previous_session.json on the executor. Wait
+      // for that to finish, otherwise it can move the session a test has just persisted. Test
+      // options set sessionFlushTimeoutMillis to 0, so waitPreviousSessionFlush() only polls.
+      val cache = options.envelopeDiskCache as EnvelopeCache
+      await.until { cache.waitPreviousSessionFlush() }
+
       capturedEnvelopes.clear()
     }
 
@@ -634,14 +640,6 @@ class InternalSentrySdkTest {
     assertThat(activeSession.get().sessionId).isNotEqualTo(oldSid)
   }
 
-  // Flaky: intermittently fails with FileNotFoundException reading session.json at the
-  // `sessionFile.reader()` call below, i.e. persistCurrentSession() did not leave a session file
-  // on disk by the time this test reads it back. Seen across unrelated PRs, e.g.:
-  // https://scans.gradle.com/s/55fnn6xhtfyfq/tests/task/:sentry-android-core:testReleaseUnitTest/details/io.sentry.android.core.InternalSentrySdkTest/updateSessionForDroppedEventNonTerminating%20flags%20an%20unhandled%20error%20without%20sending%20an%20envelope?top-execution=1
-  // https://scans.gradle.com/s/ojzzz4yxag7rw/tests/task/:sentry-android-core:testReleaseUnitTest/details/io.sentry.android.core.InternalSentrySdkTest/updateSessionForDroppedEventNonTerminating%20flags%20an%20unhandled%20error%20without%20sending%20an%20envelope?top-execution=1
-  // Disabling until root-caused; see https://github.com/getsentry/sentry-java/pull/5990 for the
-  // code under test.
-  @Ignore("Flaky: intermittently fails to find the persisted session.json, needs root-causing")
   @Test
   fun `updateSessionForDroppedEventNonTerminating flags an unhandled error without sending an envelope`() {
     val fixture = Fixture()