mongodb/jstests/noPassthrough/lock_file/lock_file.js

// The mongod process should always create a mongod.lock file in the data directory
// containing the process ID regardless of the storage engine requested.

// Ensures that mongod.lock exists and returns size of file.
function getMongodLockFileSize(dir) {
    var files = listFiles(dir);
    for (var i in files) {
        var file = files[i];
        if (!file.isDirectory && file.baseName == 'mongod.lock') {
            return file.size;
        }
    }
    assert(false, 'mongod.lock not found in data directory ' + dir);
}

var baseName = jsTestName();
var dbpath = MongoRunner.dataPath + baseName + '/';

// Test framework will append --storageEngine command line option.
var mongod = MongoRunner.runMongod({dbpath: dbpath});
assert.neq(
    0, getMongodLockFileSize(dbpath), 'mongod.lock should not be empty while server is running');

MongoRunner.stopMongod(mongod);

// mongod.lock must be empty after shutting server down.
assert.eq(0, getMongodLockFileSize(dbpath), 'mongod.lock not truncated after shutting server down');