UnhandledPromiseRejectionWarning: TypeError: Converting circular structure to JSON with Jest + Angular

Question

Using the jest-preset-angular to perform the unit test, but got an warning as UnhandledPromiseRejectionWarning: TypeError: Converting circular structure to JSON not sure what causing the error, due to this the application is stuck and not running the other unit test.

PASS  src/app/pages/result/result-filter/result-filter.component.spec.ts (6.251 s)  PASS  src/app/pages/result/search-navigation/search-navigation.component.spec.ts  PASS  src/app/pages/result/filter-modal/filter-modal.component.spec.ts (5.699 s)  PASS  src/app/app.component.spec.ts  PASS  src/app/pages/test-type/test-type.component.spec.ts (12.857 s) (node:3280) UnhandledPromiseRejectionWarning: TypeError: Converting circular structure to JSON     --> starting at object with constructor 'Object'     |     property 'element' -> object with constructor 'Object'     |     property 'componentProvider' -> object with constructor 'Object'     --- property 'parent' closes the circle     at stringify (<anonymous>)     at writeChannelMessage (internal/child_process/serialization.js:117:20)     at process.target._send (internal/child_process.js:808:17)     at process.target.send (internal/child_process.js:706:19)     at reportSuccess (/Users/macbook/Projects/Playtime Projects/IDP/Idp.Bx.Ui/idp/node_modules/jest-worker/build/workers/processChild.js:67:11) (Use `node --trace-warnings ...` to show where the warning was created) (node:3280) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1) (node:3280) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code. (node:3281) UnhandledPromiseRejectionWarning: TypeError: Converting circular structure to JSON     --> starting at object with constructor 'Object'     |     property 'element' -> object with constructor 'Object'     |     property 'componentProvider' -> object with constructor 'Object'     --- property 'parent' closes the circle     at stringify (<anonymous>)     at writeChannelMessage (internal/child_process/serialization.js:117:20)     at process.target._send (internal/child_process.js:808:17)     at process.target.send (internal/child_process.js:706:19)     at reportSuccess (/Users/macbook/Projects/Playtime Projects/IDP/Idp.Bx.Ui/idp/node_modules/jest-worker/build/workers/processChild.js:67:11) (Use `node --trace-warnings ...` to show where the warning was created) (node:3281) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1) (node:3281) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code. (node:3279) UnhandledPromiseRejectionWarning: TypeError: Converting circular structure to JSON     --> starting at object with constructor 'Object'     |     property 'element' -> object with constructor 'Object'     |     property 'componentProvider' -> object with constructor 'Object'     --- property 'parent' closes the circle     at stringify (<anonymous>)     at writeChannelMessage (internal/child_process/serialization.js:117:20)     at process.target._send (internal/child_process.js:808:17)     at process.target.send (internal/child_process.js:706:19)     at reportSuccess (/Users/macbook/Projects/Playtime Projects/IDP/Idp.Bx.Ui/idp/node_modules/jest-worker/build/workers/processChild.js:67:11) (Use `node --trace-warnings ...` to show where the warning was created) (node:3279) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1) (node:3279) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.   RUNS  src/app/pages/location/location.component.spec.ts  RUNS  src/app/pages/signup/signup.component.spec.ts  RUNS  src/app/pages/login/login.component.spec.ts  Test Suites: 10 passed, 10 of 20 total Tests:       16 passed, 16 total Snapshots:   1 obsolete, 5 passed, 5 total Time:        2180 s 

I am not sure how to run the node --trace-warnings. Looks like it a serialization issue, even it is just a warning but not sure where is the issue. Is there any better way to find the exception

Answer 1

Run jest with --detectOpenHandles. This will show you what is actually wrong with your test spec. For me, there were missing Angular Material imports and service mocks. You may be prompted to add the BrowserAnimationsModule, as Nambi alluded to in his answer

package.json:

"test": "jest --detectOpenHandles"