You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: main.rs
    path of file: ./repos/exonum/services/time/examples/simple_service
    
    the code of the file until where you have to start completion: // Copyright 2020 The Exonum Team
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under
    
fn main() {
    let mock_provider = Arc::new(MockTimeProvider::default());
    // Create testkit for network with one validator.
    let time_service =
        TimeServiceFactory::with_provider(mock_provider.clone() as Arc<dyn TimeProvider>);
    let time_service =
        Spec::new(time_service).with_instance(TIME_SERVICE_ID, TIME_SERVICE_NAME, ());
    let marker_service = Spec::new(MarkerService).with_instance(SERVICE_ID, SERVICE_NAME, ());

    let mut testkit = TestKitBuilder::validator()
        .with(time_service)
        .with(marker_service)
        .build();

    mock_provider.set_time(OffsetDateTime::from_unix_timestamp(10).unwrap());
    testkit.create_blocks_until(Height(2));

    let snapshot = testkit.snapshot();
    let time_schema: TimeSchema<_> = snapshot.service_schema(TIME_SERVICE_NAME).unwrap();
    assert_eq!(time_schema.time.get(), Some(mock_provider.time()));

    let keypair1 = KeyPair::random();
    let keypair2 = KeyPair::random();
    let keypair3 = KeyPair::random();
    let tx1 = keypair1.mark(SERVICE_ID, TxMarker::new(1, mock_provider.time()));
    let tx2 = keypair2.mark(
        SERVICE_ID,
        TxMarker::new(2, mock_provider.time() + Duration::seconds(10)),
    );
    let tx3 = keypair3.mark(
        SERVICE_ID,
        TxMarker::new(3, mock_provider.time() - Duration::seconds(5)),
    );
    testkit.create_block_with_transactions(vec![tx1, tx2, tx3]);

    let snapshot = testkit.snapshot();
    let schema: MarkerSchema<_> = snapshot.service_schema(SERVICE_NAME).unwrap();
    assert_eq!(schema.marks.get(&keypair1.public_key()), Some(1));
    assert_eq!(schema.marks.get(&keypair2.public_key()), Some(2));
    assert_eq!(schema.marks.get(&keypair3.public_key()), None);

    let tx4 = keypair3.mark(
        SERVICE_ID,
        TxMarker::new(4, OffsetDateTime::from_unix_timestamp(15).unwrap()),
    );
    testkit.create_block_with_transactions(vec![tx4]);

    let snapshot = testkit.snapshot();
    let schema: MarkerSchema<_> = snapshot.service_schema(SERVICE_NAME).unwrap();
    assert_eq!(schema.marks.get(&keypair3.public_key()), Some(4));
}