test/unit/ipc/reader/zero-column-batch-tests.ts

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import '../../../jest-extensions.js';
import {
    makeData,
    RecordBatch,
    RecordBatchStreamWriter,
    Schema,
    Struct,
    tableFromIPC,
} from 'apache-arrow';

/** Helper to create a zero-column IPC stream buffer with the given number of rows. */
function createZeroColumnIPCBuffer(numRows: number): Uint8Array {
    const schema = new Schema([]);
    const data = makeData({
        type: new Struct([]),
        length: numRows,
        nullCount: 0,
        children: [],
    });
    const batch = new RecordBatch(schema, data);
    const writer = new RecordBatchStreamWriter();
    writer.write(batch);
    writer.finish();
    return writer.toUint8Array(true);
}

describe('Zero-column RecordBatch numRows preservation', () => {

    describe('IPC round-trip', () => {

        test('should read zero-column stream and preserve numRows', () => {
            const buffer = createZeroColumnIPCBuffer(100);
            const table = tableFromIPC(buffer);

            expect(table.numRows).toBe(100);
            expect(table.numCols).toBe(0);
            expect(table.batches).toHaveLength(1);
            expect(table.batches[0].numRows).toBe(100);
        });
    });

    describe('Direct constructor', () => {

        test('RecordBatch constructor preserves length for zero-column data', () => {
            const schema = new Schema([]);
            const data = makeData({
                type: new Struct([]),
                length: 100,
                nullCount: 0,
                children: [],
            });
            const batch = new RecordBatch(schema, data);

            expect(batch.numRows).toBe(100);
            expect(batch.numCols).toBe(0);
        });
    });
});