Test typescript async function using Jest

I have the following code in main typescript file:

public readonly funcname = async (
param: string): Promise<CustomeType> => {
  const constname = somefunction(strparam, jsonparam);
  return Promise.resolve({
     reqname:constname
  });
};

This is written under an exported class say exportedservice.

I am writing the following testcase in jest for same:

const outputMock = jest.fn(()=>{
  return Promise.reject()
});

const exportedserviceobj = new exportedservice()
describe("Statement", () => {
it("statement", async () => {
   expect.assertions(1);
   const outputResult = await exportedserviceobj.funcname("TestFile")
   outputMock().then(outputResult);
   expect(outputResult).tobeEqual("undefined")
  });
});

while running the test case; it is throwing a type error:

exportedservice.funcname is not a function

As I am new to typescript; so after a lot of R&D; I am unable to resolve the issue. Please suggest appropriate way to solve this out. Thanks in Advance.