diff --git a/src/repositories/shuttle/eta/__tests__/ExternalSourceETARepositorySharedTests.test.ts b/src/repositories/shuttle/eta/__tests__/ExternalSourceETARepositorySharedTests.test.ts
new file mode 100644
index 0000000..4dc4980
--- /dev/null
+++ b/src/repositories/shuttle/eta/__tests__/ExternalSourceETARepositorySharedTests.test.ts
@@ -0,0 +1,151 @@
+import { afterEach, beforeEach, describe, expect, test } from "@jest/globals";
+import { RepositoryHolder } from "../../../../../testHelpers/RepositoryHolder";
+import { ExternalSourceETARepository } from "../ExternalSourceETARepository";
+import { RedisExternalSourceETARepository } from "../RedisExternalSourceETARepository";
+import { generateMockEtas } from "../../../../../testHelpers/mockDataGenerators";
+
+class RedisExternalSourceETARepositoryHolder implements RepositoryHolder<ExternalSourceETARepository> {
+  repo: RedisExternalSourceETARepository | undefined;
+
+  name = "RedisExternalSourceETARepository"
+  factory = async () => {
+    this.repo = new RedisExternalSourceETARepository();
+    await this.repo.connect();
+    return this.repo;
+  }
+  teardown = async () => {
+    if (this.repo) {
+      await this.repo.clearAllData();
+      await this.repo.disconnect();
+    }
+  }
+}
+
+const repositoryImplementations = [
+  new RedisExternalSourceETARepositoryHolder()
+];
+
+describe.each(repositoryImplementations)('$name', (holder) => {
+  let repository: ExternalSourceETARepository;
+  
+  beforeEach(async () => {
+    repository = await holder.factory();
+  });
+
+  afterEach(async () => {
+    await holder.teardown();
+  });
+
+  describe("addOrUpdateEtaFromExternalSource", () => {
+    test("adds a new ETA if nonexistent", async () => {
+      const mockEtas = generateMockEtas();
+      const newEta = mockEtas[0];
+
+      await repository.addOrUpdateEtaFromExternalSource(newEta);
+
+      const result = await repository.getEtasForShuttleId(newEta.shuttleId);
+      expect(result).toEqual([newEta]);
+    });
+
+    test("updates an existing ETA if it exists", async () => {
+      const mockEtas = generateMockEtas();
+      const existingEta = mockEtas[0];
+      const updatedEta = structuredClone(existingEta);
+      updatedEta.secondsRemaining = existingEta.secondsRemaining + 60;
+
+      await repository.addOrUpdateEtaFromExternalSource(existingEta);
+      await repository.addOrUpdateEtaFromExternalSource(updatedEta);
+
+      const result = await repository.getEtasForShuttleId(existingEta.shuttleId);
+      expect(result).toEqual([updatedEta]);
+    });
+  });
+
+  describe("getEtasForShuttleId", () => {
+    test("gets ETAs for a specific shuttle ID", async () => {
+      const mockEtas = generateMockEtas();
+      for (const eta of mockEtas) {
+        await repository.addOrUpdateEtaFromExternalSource(eta);
+      }
+
+      const result = await repository.getEtasForShuttleId("sh1");
+      const expected = mockEtas.filter((eta) => eta.shuttleId === "sh1");
+      expect(result).toHaveLength(expected.length);
+      expect(result).toEqual(expect.arrayContaining(expected));
+    });
+
+    test("returns an empty list if there are no ETAs for the shuttle ID", async () => {
+      const result = await repository.getEtasForShuttleId("nonexistent-shuttle");
+      expect(result).toEqual([]);
+    });
+  });
+
+  describe("getEtasForStopId", () => {
+    test("gets ETAs for a specific stop ID", async () => {
+      const mockEtas = generateMockEtas();
+      for (const eta of mockEtas) {
+        await repository.addOrUpdateEtaFromExternalSource(eta);
+      }
+
+      const result = await repository.getEtasForStopId("st1");
+      expect(result).toEqual(mockEtas.filter((eta) => eta.stopId === "st1"));
+    });
+
+    test("returns an empty list if there are no ETAs for the stop ID", async () => {
+      const result = await repository.getEtasForStopId("nonexistent-stop");
+      expect(result).toEqual([]);
+    });
+  });
+
+  describe("getEtaForShuttleAndStopId", () => {
+    test("gets a single ETA for a specific shuttle and stop ID", async () => {
+      const mockEtas = generateMockEtas();
+      const mockEta = mockEtas[0];
+      await repository.addOrUpdateEtaFromExternalSource(mockEta);
+
+      const result = await repository.getEtaForShuttleAndStopId("sh1", "st1");
+      expect(result).toEqual(mockEta);
+    });
+
+    test("returns null if no ETA matches the shuttle and stop ID", async () => {
+      const result = await repository.getEtaForShuttleAndStopId("nonexistent-shuttle", "nonexistent-stop");
+      expect(result).toBeNull();
+    });
+  });
+
+  describe("removeEtaIfExists", () => {
+    test("removes eta given shuttle ID and stop ID", async () => {
+      let mockEtas = generateMockEtas();
+      const stopId = mockEtas[0].stopId;
+      mockEtas = mockEtas.filter((eta) => eta.stopId === stopId);
+
+      await Promise.all(mockEtas.map(async (eta) => {
+        eta.stopId = stopId;
+        await repository.addOrUpdateEtaFromExternalSource(eta);
+      }));
+
+      const etaToRemove = mockEtas[0];
+      await repository.removeEtaIfExists(etaToRemove.shuttleId, etaToRemove.stopId);
+
+      const remainingEtas = await repository.getEtasForStopId(stopId);
+      expect(remainingEtas).toHaveLength(mockEtas.length - 1);
+    });
+
+    test("does nothing if eta doesn't exist", async () => {
+      let mockEtas = generateMockEtas();
+      const stopId = mockEtas[0].stopId;
+      mockEtas = mockEtas.filter((eta) => eta.stopId === stopId);
+
+      await Promise.all(mockEtas.map(async (eta) => {
+        eta.stopId = stopId;
+        await repository.addOrUpdateEtaFromExternalSource(eta);
+      }));
+
+      await repository.removeEtaIfExists("nonexistent-shuttle-id", "nonexistent-stop-id");
+
+      const remainingEtas = await repository.getEtasForStopId(stopId);
+      expect(remainingEtas).toHaveLength(mockEtas.length);
+    });
+  });
+})
+