TEST_F(StepDownTest, OnlyOneStepDownCmdIsAllowedAtATime) {
    OpTime optime1(Timestamp(100, 1), 1);
    OpTime optime2(Timestamp(100, 2), 1);

    // No secondary is caught up
    auto repl = getReplCoord();
    repl->setMyLastAppliedOpTime(optime2);
    repl->setMyLastDurableOpTime(optime2);
    ASSERT_OK(repl->setLastAppliedOptime_forTest(1, 1, optime1));
    ASSERT_OK(repl->setLastAppliedOptime_forTest(1, 2, optime1));

    simulateSuccessfulV1Election();

    ASSERT_TRUE(getReplCoord()->getMemberState().primary());

    // Step down where the secondary actually has to catch up before the stepDown can succeed.
    // On entering the network, _stepDownContinue should cancel the heartbeats scheduled for
    // T + 2 seconds and send out a new round of heartbeats immediately.
    // This makes it unnecessary to advance the clock after entering the network to process
    // the heartbeat requests.
    auto result = stepDown_nonBlocking(false, Seconds(10), Seconds(60));

    // Now while the first stepdown request is waiting for secondaries to catch up, attempt another
    // stepdown request and ensure it fails.
    const auto opCtx = makeOperationContext();
    auto status = getReplCoord()->stepDown(opCtx.get(), false, Seconds(10), Seconds(60));
    ASSERT_EQUALS(ErrorCodes::ConflictingOperationInProgress, status);

    // Now ensure that the original stepdown command can still succeed.
    catchUpSecondaries(optime2);

    ASSERT_OK(*result.second.get());
    ASSERT_TRUE(repl->getMemberState().secondary());
}