Errors thrown from assert() are not readable in tests

[myflowpl]

Errors from assert() function are not helpful in stack trace when testing with jest

    async getOne<T>(spec: QuerySpecification<T>): Promise<T> {
        const results = await this.persistenceManager.query(spec);
        assert(results.length === 1, `Expected exactly one result`);
        return results[0];
    }

In tests doesn't say what happened

FAIL  libs/api/db/src/lib/user/user.repository.spec.ts
  ● UserRepository › .update() › should update user

    assert(received)

    Expected value to be equal to:
      true
    Received:
      false

    Message:
      Expected exactly one result

      71 |       const data = await userFixture.createFakeUser();
      72 |       const name = 'new name'
    > 73 |       const updated = await userRepository.update(data.rid, {name});
         |                       ^
      74 | 
      75 |       const res: UserEntity = {
      76 |         rid: expect.any(String),

      at FinderOperations.getOne (../../../node_modules/@liberation-data/src/manager/FinderOperations.ts:11:9)
      at TransactionalPersistenceManager.getOne (../../../node_modules/@liberation-data/src/manager/TransactionalPersistenceManager.ts:23:16)        
      at runInTransaction (../../../node_modules/@liberation-data/src/transaction/Transactional.ts:39:24)
      at src/lib/user/user.repository.spec.ts:73:23

We should always use custom errors like we do here:

    async maybeGetOne<T>(spec: QuerySpecification<T>): Promise<T | undefined> {
        const results = await this.persistenceManager.query(spec);
        if (results.length === 0) {
            return undefined;
        } else if (results.length === 1) {
            return results[0];
        } else {
            throw new DrivineError(`Expected one result, received ${results.length}.`);
        }
    }