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: project.rs
    path of file: ./repos/risingwave/src/stream/src/executor
    
    the code of the file until where you have to start completion: // Copyright 2024 RisingWave Labs
//
// 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 the License.

use std::fmt::{Debug, Formatter};

use futures::StreamExt;
use futures_async_stream::try_stream;
use multimap::MultiMap;
use risingwave_common::array::StreamChunk;
use risingwave_common::row::{Row, RowExt};
us
    
    async fn test_watermark_projection() {
        let schema = Schema {
            fields: vec![
                Field::unnamed(DataType::Int64),
                Field::unnamed(DataType::Int64),
            ],
        };
        let (mut tx, source) = MockSource::channel();
        let source = source.into_executor(schema, PkIndices::new());

        let a_expr = build_from_pretty("(add:int8 $0:int8 1:int8)");
        let b_expr = build_from_pretty("(subtract:int8 $0:int8 1:int8)");
        let c_expr = NonStrictExpression::for_test(DummyNondecreasingExpr);

        let project = ProjectExecutor::new(
            ActorContext::for_test(123),
            source,
            vec![a_expr, b_expr, c_expr],
            MultiMap::from_iter(vec![(0, 0), (0, 1)].into_iter()),
            vec![2],
            0.0,
        );
        let mut project = project.boxed().execute();

        tx.push_barrier(test_epoch(1), false);
        tx.push_int64_watermark(0, 100);

        project.expect_barrier().await;
        let w1 = project.expect_watermark().await;
        let w2 = project.expect_watermark().await;
        let (w1, w2) = if w1.col_idx < w2.col_idx {
            (w1, w2)
        } else {
            (w2, w1)
        };

        assert_eq!(
            w1,
            Watermark {
                col_idx: 0,
                data_type: DataType::Int64,
                val: ScalarImpl::Int64(101)
            }
        );
        assert_eq!(
            w2,
            Watermark {
                col_idx: 1,
                data_type: DataType::Int64,
                val: ScalarImpl::Int64(99)
            }
        );

        // just push some random chunks
        tx.push_chunk(StreamChunk::from_pretty(
            "   I I
            + 120 4
            + 146 5
            + 133 6",
        ));
        project.expect_chunk().await;
        tx.push_chunk(StreamChunk::from_pretty(
            "   I I
            + 213 8
            - 133 6",
        ));
        project.expect_chunk().await;

        tx.push_barrier(test_epoch(2), false);
        let w3 = project.expect_watermark().await;
        project.expect_barrier().await;

        tx.push_chunk(StreamChunk::from_pretty(
            "   I I
            + 100 3
            + 104 5
            + 187 3",
        ));
        project.expect_chunk().await;

        tx.push_barrier(test_epoch(3), false);
        let w4 = project.expect_watermark().await;
        project.expect_barrier().await;

        assert_eq!(w3.col_idx, w4.col_idx);
        assert!(w3.val.default_cmp(&w4.val).is_le());

        tx.push_int64_watermark(1, 100);
        tx.push_barrier(test_epoch(4), true);

        assert!(project.next().await.unwrap().unwrap().is_stop());
    }