mongodb/jstests/sharding/change_stream_no_shards.js

/**
 * Test that running a $changeStream aggregation on a cluster with no shards returns an empty result
 * set with a cursorID of zero.
 */
(function() {
    const st = new ShardingTest({shards: 0, config: 1});

    const adminDB = st.s.getDB("admin");
    const testDB = st.s.getDB("test");

    // Test that attempting to open a stream on a single collection results in an empty, closed
    // cursor response.
    let csCmdRes = assert.commandWorked(
        testDB.runCommand({aggregate: "testing", pipeline: [{$changeStream: {}}], cursor: {}}));
    assert.docEq(csCmdRes.cursor.firstBatch, []);
    assert.eq(csCmdRes.cursor.id, 0);

    // Test that attempting to open a whole-db stream results in an empty, closed cursor response.
    csCmdRes = assert.commandWorked(
        testDB.runCommand({aggregate: 1, pipeline: [{$changeStream: {}}], cursor: {}}));
    assert.docEq(csCmdRes.cursor.firstBatch, []);
    assert.eq(csCmdRes.cursor.id, 0);

    // Test that attempting to open a cluster-wide stream results in an empty, closed cursor
    // response.
    csCmdRes = assert.commandWorked(adminDB.runCommand(
        {aggregate: 1, pipeline: [{$changeStream: {allChangesForCluster: true}}], cursor: {}}));
    assert.docEq(csCmdRes.cursor.firstBatch, []);
    assert.eq(csCmdRes.cursor.id, 0);

    // Test that a regular, non-$changeStream aggregation also results in an empty cursor when no
    // shards are present.
    const nonCsCmdRes = assert.commandWorked(
        testDB.runCommand({aggregate: "testing", pipeline: [{$match: {}}], cursor: {}}));
    assert.docEq(nonCsCmdRes.cursor.firstBatch, []);
    assert.eq(nonCsCmdRes.cursor.id, 0);

    st.stop();
})();