How to write a test which expects an Error to be thrown in Jasmine

Question

I m trying to write a test for the Jasmine Test Framework which expects an error  At the moment I m using a Jasmine Node js integration from GitHub   In my Node module I have the following code   throw new Error  Parsing is not possible      Now I try to write a test which expects this error   describe  my suite      function                  it  should not parse foo   function                      expect parser parse raw   toThrow new Error  Parsing is not possible                   I tried also Error   and some other variants and just can t figure out how to make it work

User · Answer

As mentioned previously  a function needs to be passed to toThrow as it is the function you re describing in your test   I expect this function to throw x   expect      gt  parser parse raw      toThrow new Error  Parsing is not possible       If using Jasmine-Matchers you can also use one of the following when they suit the situation      I just want to know that an error was    thrown and nothing more about it expect      gt  parser parse raw      toThrowAnyError      or     I just want to know that an error of     a given type was thrown and nothing more expect      gt  parser parse raw      toThrowErrorOfType TypeError

User · Answer

For coffeescript lovers  expect    gt  someMethodCall arg1  arg2   toThrow

User · Answer

In my case the function throwing error was async so I followed here  await expectAsync asyncFunction    toBeRejected    await expectAsync asyncFunction    toBeRejectedWithError

User · Answer

For anyone who still might be facing this issue  for me the posted solution didn t work and it kept on throwing this error  Error  Expected function to throw an exception  I later realised that the function which I was expecting to throw an error was an async function and was expecting promise to be rejected and then throw error and that s what I was doing in my code    throw new Error  REQUEST ID NOT FOUND      and thats what I did in my test and it worked   it  Test should throw error if request not found   willResolve      gt             const promise   service getRequestStatus  request-id                    return expectToReject promise  then  err    gt                        expect err message  toEqual  REQUEST NOT FOUND

User · Answer

I know that is more code but you can also do   try    do something     fail Error  should send a Exception    catch e    expect e name  toBe  BLA ERROR     expect e message  toBe  Message

User · Answer

A more elegant solution than creating an anonymous function who s sole purpose is to wrap another  is to use es5 s bind function  The bind function creates a new function that  when called  has its this keyword set to the provided value  with a given sequence of arguments preceding any provided when the new function is called   Instead of   expect function      parser parse raw  config       toThrow  Parsing is not possible     Consider   expect parser parse bind parser  raw  config   toThrow  Parsing is not possible     The bind syntax allows you to test functions with different this values  and in my opinion makes the test more readable  See also  https   stackoverflow com a 13233194 1248889

User · Answer

You are using   expect fn  toThrow e    But if you ll have a look on the function comment  expected is string    294     295    Matcher that checks that the expected exception was thrown by the actual  296    297     param  String  expected 298     299 jasmine Matchers prototype toThrow   function expected      I suppose you should probably write it like this  using lambda - anonymous function    expect function     parser parse raw       toThrow  Parsing is not possible      This is confirmed in the following example   expect function     throw new Error  Parsing is not possible     toThrow  Parsing is not possible      Douglas Crockford strongly recommends this approach  instead of using  throw new Error     prototyping way    throw      name   Error      message   Parsing is not possible

User · Answer

I replace Jasmine s toThrow matcher with the following  which lets you match on the exception s name property or its message property   For me this makes tests easier to write and less brittle  as I can do the following   throw      name   NoActionProvided      message   Please specify an  action  property when configuring the action map       and then test with the following   expect  function            do something    toThrow   NoActionProvided      This lets me tweak the exception message later without breaking tests  when the important thing is that it threw the expected type of exception   This is the replacement for toThrow that allows this   jasmine Matchers prototype toThrow   function expected      var result   false    var exception    if  typeof this actual     function         throw new Error  Actual is not a function          try       this actual        catch  e        exception   e        if  exception          result    expected     jasmine undefined    this env equals  exception message    exception  expected message    expected     this env equals  exception name  expected           var not   this isNot    not            this message   function         if  exception  amp  amp   expected     jasmine undefined     this env equals  exception message    exception  expected message    expected            return   Expected function     not    to throw   expected   expected name    expected message    expected     an exception      but it threw   exception name    exception message    exception  join             else         return  Expected function to throw an exception                  return result

User · Answer

Try using an anonymous function instead   expect  function    parser parse raw       toThrow new Error  Parsing is not possible       you should be passing a function into the expect      call  Your incorrect code      incorrect  expect parser parse raw   toThrow new Error  Parsing is not possible       is trying to actually call parser parse raw  in an attempt to pass the result into expect

[javascript] How to write a test which expects an Error to be thrown in Jasmine?

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