tapgarden: use require.Eventually in assertPendingBatchExists

Refactor assertPendingBatchExists to use require.Eventually, allowing
additional time for the state machine to reach the expected state. This
improves test reliability by reducing flakiness and making the unit test
more robust.

Author: ffranr

tapgarden/planter_test.go

@@ -318,10 +318,15 @@ func (t *mintingTestHarness) queueSeedlingsInBatch(isFunded bool,
 func (t *mintingTestHarness) assertPendingBatchExists(numSeedlings int) {
 	t.Helper()
 
-	batch, err := t.planter.PendingBatch()
-	require.NoError(t, err)
-	require.NotNil(t, batch)
-	require.Len(t, batch.Seedlings, numSeedlings)
+	// The planter is a state machine, so we need to wait until it has
+	// reached the expected state.
+	require.Eventually(t, func() bool {
+		batch, err := t.planter.PendingBatch()
+		require.NoError(t, err)
+
+		require.NotNil(t, batch)
+		return len(batch.Seedlings) == numSeedlings
+	}, defaultTimeout, wait.PollInterval)
 }
 
 // assertNoActiveBatch asserts that no pending batch exists.