# test.govlab/patterns/core/aggregators/representation.sequence.aggregator.test.ts

> 24 lines of code and 0 definitions.

Tree: Codebase Testing
Language: typescript
Canonical: https://banes-lab.com/anatomy/testing#file-testing-test-govlab-patterns-core-aggregators-representation-sequence-aggregator-test-ts
Source text: https://banes-lab.com/source/testing/test.govlab/patterns/core/aggregators/representation.sequence.aggregator.test.ts.txt

Listed in [test.govlab/patterns/core/aggregators](https://banes-lab.com/api/source/testing/test.govlab/patterns/core/aggregators.md), after [test.govlab/patterns/core/aggregators/representation.grid.aggregator.test.ts](https://banes-lab.com/source/testing/test.govlab/patterns/core/aggregators/representation.grid.aggregator.test.ts.md) and before [test.govlab/patterns/core/aggregators/representation.tree.aggregator.test.ts](https://banes-lab.com/source/testing/test.govlab/patterns/core/aggregators/representation.tree.aggregator.test.ts.md).

## Contained in

- [test.govlab/patterns/core/aggregators](https://banes-lab.com/anatomy/testing/folder-testing-test-govlab-patterns-core-aggregators.md)

## Source

```typescript
import { describe, expect, it } from "vitest";
import { SequenceAccumulator } from "@govlab/patterns/core/aggregators/representation.sequence.aggregator.ts";
import { createRng } from "@govlab/patterns/core/factories/seed.factory.ts";

const SEED = 3;

describe("SequenceAccumulator", () => {
    it("tracks runs, transitions and the last value", () => {
        const accumulator = new SequenceAccumulator("state");
        accumulator.update([{ state: "a" }, { state: "a" }, { state: "b" }, { state: "a" }]);
        const summary = accumulator.result();
        expect(summary.longestRun).toBe(2);
        expect(summary.lastValue).toBe("a");
        expect(summary.topTransitions.map(([pair]) => pair)).toContainEqual(["a", "b"]);
        expect(summary.runLengths).toStrictEqual([
            [1, 2],
            [2, 1],
        ]);
    });

    it("samples a seen value, and nothing before any value", () => {
        const accumulator = new SequenceAccumulator("state");
        expect(accumulator.sample(createRng(SEED))).toBeNull();
        accumulator.update([{ state: "a" }]);
        expect(accumulator.sample(createRng(SEED))).toBe("a");
    });
});
```