move json syntax error setting to top-level method

test/loaders/ApiBasedRepositoryLoaderTests.test.ts

@@ -41,6 +41,17 @@ async function assertAsyncCallbackThrowsApiResponseError(callback: () => Promise
   await expect(callback).rejects.toThrow(ApiResponseError);
 }
 
+function updateGlobalFetchMockJsonToThrowSyntaxError() {
+  // @ts-ignore
+  global.fetch = jest.fn(() => {
+    return Promise.resolve({
+      json: () => Promise.reject(new SyntaxError("Unable to parse JSON")),
+      status: 200,
+      ok: true,
+    })
+  }) as jest.Mock;
+}
+
 describe("ApiBasedRepositoryLoader", () => {
   let loader: ApiBasedRepositoryLoader;
 
@@ -122,14 +133,7 @@ describe("ApiBasedRepositoryLoader", () => {
       // The Passio API returns some invalid JSON if there is no data,
       // so simulate a JSON parsing error
 
-      // @ts-ignore
+      updateGlobalFetchMockJsonToThrowSyntaxError();
-      global.fetch = jest.fn(() => {
-        return Promise.resolve({
-          json: () => Promise.reject(new SyntaxError("Unable to parse JSON")),
-          status: 200,
-          ok: true,
-        })
-      }) as jest.Mock;
 
       await assertAsyncCallbackThrowsApiResponseError(async () => {
         await loader.fetchAndUpdateRouteDataForSystemId("263");
@@ -160,14 +164,7 @@ describe("ApiBasedRepositoryLoader", () => {
     });
 
     it("throws the correct error if the API response contains no data", async () => {
-      // @ts-ignore
+      updateGlobalFetchMockJsonToThrowSyntaxError();
-      global.fetch = jest.fn(() => {
-        return Promise.resolve({
-          json: () => Promise.reject(new SyntaxError("Unable to parse JSON")),
-          status: 200,
-          ok: true,
-        })
-      }) as jest.Mock;
 
       await assertAsyncCallbackThrowsApiResponseError(async () => {
         await loader.fetchAndUpdateStopAndPolylineDataForRoutesWithSystemId("263");