How to write unit testing for Angular TypeScript for private methods with Jasmine

Question

How do you test a private function in angular 2    class FooBar        private  status  number       constructor  private foo   Bar             this initFooBar                private initFooBar            this foo bar   data             this  status   this fooo foo               public get status            return this  status             The solution I found    Put the test code itself inside the closure or Add code inside the closure that stores references to the local variables on existing objects in the outer scope    Later strip out the test code using a tool  http   philipwalton com articles how-to-unit-test-private-functions-in-javascript    Please suggest me a better way to solve this problem if you have done any   P S    Most of the answer for similar type of question like this one doesn t give a solution to problem  that s why I m asking this question Most of the developer say you Don   t test private functions but I don t say they are wrong or right  but there are necessities for my case to test private

User · Answer

You can call private methods  If you encountered the following error  expect new FooBar          initFooBar    toEqual              TS2341  Property  initFooBar  is private and only accessible within class  FooBar   just use     ts-ignore      ts-ignore expect new FooBar          initFooBar    toEqual

User · Answer

The answer by Aaron is the best and is working for me    I would vote it up but sadly I can t  missing reputation    I ve to say testing private methods is the only way to use them and have clean code on the other side   For example   class Something     save        const data   this getAllUserData       if  this validate data         this sendRequest data        private getAllUserData            private validate data          private sendRequest data            It  makes a lot of sense to not test all these methods at once because we would need to mock out those private methods  which we can t mock out because we can t access them  This means we need a lot of configuration for a unit test to test this as a whole   This said the best way to test the method above with all dependencies is an end to end test  because here an integration test is needed  but the E2E test won t help you if you are practicing TDD  Test Driven Development   but testing any method will

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Sorry for the necro on this post  but I feel compelled to weigh in on a couple of things that do not seem to have been touched on   First a foremost - when we find ourselves needing access to private members on a class during unit testing  it is generally a big  fat red flag that we ve goofed in our strategic or tactical approach and have inadvertently violated the single responsibility principal by pushing behavior where it does not belong  Feeling the need to access methods that are really nothing more than an isolated subroutine of a construction procedure is one of the most common occurrences of this  however  it s kind of like your boss expecting you to show up for work ready-to-go and also having some perverse need to know what morning routine you went through to get you into that state     The other most common instance of this happening is when you find yourself trying to test the proverbial  god class   It is a special kind of problem in and of itself  but suffers from the same basic issue with needing to know intimate details of a procedure - but that s getting off topic   In this specific example  we ve effectively assigned the responsibility of fully initializing the Bar object to the FooBar class s constructor  In object oriented programming  one of the core tenents is that the constructor is  sacred  and should be guarded against invalid data that would invalidate its  own internal state and leave it primed to fail somewhere else downstream  in what could be a very deep pipeline     We ve failed to do that here by allowing the FooBar object to accept a Bar that is not ready at the time that the FooBar is constructed  and have compensated by sort-of  hacking  the FooBar object to take matters into its  own hands    This is the result of a failure to adhere to another tenent of object oriented programming  in the case of Bar   which is that an object s state should be fully initialized and ready to handle any incoming calls to its  public members immediately after creation  Now  this does not mean immediately after the constructor is called in all instances  When you have an object that has many complex construction scenarios  then it is better to expose setters to its optional members to an object that is implemented in accordance with a creation design-pattern  Factory  Builder  etc     In any of the latter cases  you would be pushing the initialization of the target object off into another object graph whose sole purpose is directing traffic to get you to a point where you have a valid instance of that which you are requesting - and the product should not be considered  ready  until after this creation object has served it up    In your example  the Bar s  status  property does not seem to be in a valid state in which a FooBar can accept it - so the FooBar does something to it to correct that issue    The second issue I am seeing is that it appears that you are trying to test your code rather than practice test-driven development  This is definitely my own opinion at this point in time  but  this type of testing is really an anti-pattern  What you end up doing is falling into the trap of realizing that you have core design problems that prevent your code from being testable after the fact  rather than writing the tests you need and subsequently programming to the tests  Either way you come at the problem  you should still end up with the same number of tests and lines of code had you truly achieved a SOLID implementation  So - why try and reverse engineer your way into testable code when you can just address the matter at the onset of your development efforts    Had you done that  then you would have realized much earlier on that you were going to have to write some rather icky code in order to test against your design and would have had the opportunity early on to realign your approach by shifting behavior to implementations that are easily testable

User · Answer

As most of the developers don t recommend testing private function  Why not test it     Eg   YourClass ts  export class FooBar     private  status  number     constructor  private foo   Bar         this initFooBar             private initFooBar data       this foo bar  data        this  status   this foo foo            TestYourClass spec ts  describe  Testing foo bar for status being set   function             Variable with type any let fooBar   fooBar   new FooBar           Method 1   Now this will be visible fooBar initFooBar       Method 2   This doesn t require variable with any type fooBar  initFooBar               Thanks to  Aaron   Thierry Templier

User · Answer

This worked for me   Instead of   sut myPrivateMethod      This   sut  myPrivateMethod

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This route I take is one where I create functions outside the class and assign the function to my private method    export class MyClass     private  myPrivateFunction   someFunctionThatCanBeTested     function someFunctionThatCanBeTested         This Is Testable     Now I don t know what type of OOP rules I am breaking  but to answer the question  this is how I test private methods  I welcome anyone to advise on Pros  amp  Cons of this

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I agree with  toskv  I wouldn t recommend to do that -   But if you really want to test your private method  you can be aware that the corresponding code for the TypeScript correspond to a method of the constructor function prototype  This means that it can be used at runtime  whereas you will probably have some compilation errors    For example   export class FooBar     private  status  number     constructor  private foo   Bar         this initFooBar             private initFooBar data       this foo bar  data        this  status   this foo foo            will be transpiled into    function System    function   moduleName  System register     function exports 1  context 1       use strict     var   moduleName   context 1  amp  amp  context 1 id    var FooBar    return       setters         execute  function           FooBar    function              function FooBar foo              this foo   foo            this initFooBar                        FooBar prototype initFooBar   function  data              this foo bar data             this  status   this foo foo                       return FooBar                    exports 1  FooBar   FooBar                System     See this plunkr  https   plnkr co edit calJCF p preview

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I m with you  even though it s a good goal to  only unit test the public API  there are times when it doesn t seem that simple and you feel you are choosing between compromising either the API or the unit-tests  You know this already  since that s exactly what you re asking to do  so I won t get into it      In TypeScript I ve discovered a few ways you can access private members for the sake of unit-testing  Consider this class   class MyThing        private  name string      private  count number       constructor             this init  Test   123              private init name string  count number           this  name   name          this  count   count             public get name    return this  name         public get count    return this  count         Even though TS restricts access to class members using private  protected  public  the compiled JS has no private members  since this isn t a thing in JS  It s purely used for the TS compiler  Therefor    You can assert to any and escape the compiler from warning you about access restrictions    thing as any   name    Unit Test    thing as any   count   123   thing as any  init  Unit Test   123     The problem with this approach is that the compiler simply has no idea what you are doing right of the any  so you don t get desired type errors    thing as any   name   123     wrong  but no error  thing as any   count    Unit Test      wrong  but no error  thing as any  init 0   123       wrong  but no error   This will obviously make refactoring more difficult  You can use array access      to get at the private members   thing   name      Unit Test   thing   count     123  thing  init    Unit Test   123     While it looks funky  TSC will actually validate the types as if you accessed them directly   thing   name     123     type error thing   count      Unit Test      type error thing  init   0   123       argument error   To be honest I don t know why this works  This is apparently an intentional  escape hatch  to give you access to private members without losing type safety  This is exactly what I think you want for your unit-testing    Here is a working example in the TypeScript Playground   Edit for TypeScript 2 6  Another option that some like is to use     ts-ignore  added in TS 2 6  which simply suppresses all errors on the following line       ts-ignore thing  name    Unit Test     The problem with this is  well  it suppresses all errors on the following line       ts-ignore thing  name 123  this should NOT beAllowed  but it is     window         I personally consider  ts-ignore a code-smell  and as the docs say      we recommend you use this comments very sparingly   emphasis original

User · Answer

As many have already stated  as much as you want to test the private methods you shouldn t hack your code or transpiler to make it work for you  Modern day TypeScript will deny most all of the hacks that people have provided so far     Solution  TLDR  if a method should be tested then you should be decoupling the code into a class that you can expose the method to be public to be tested    The reason you have the method private is because the functionality doesn t necessarily belong to be exposed by that class  and therefore if the functionality doesn t belong there it should be decoupled into it s own class   Example  I ran across this article that does a great job of explaining how you should tackle testing private methods  It even covers some of the methods here and how why they re bad implementations   https   patrickdesjardins com blog how-to-unit-test-private-method-in-typescript-part-2  Note  This code is lifted from the blog linked above  I m duplicating in case the content behind the link changes   Before  class User      public getUserInformationToDisplay                          this getUserAddress                             private getUserAddress                          this formatStreet                            private formatStreet                            After  class User      private address Address      public getUserInformationToDisplay                          address getUserAddress                          class Address      private format  StreetFormatter      public format                          format ToString                          class StreetFormatter      public toString

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call private method using square brackets   Ts file  class Calculate    private total    private add a  number          return a   total          spect ts file  it  should return 5 if input 3 and 2        gt        component  total     2      let result   component  add   3       expect result  toEqual 5

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The point of  don t test private methods  really is Test the class like someone who uses it   If you have a public API with 5 methods  any consumer of your class can use these  and therefore you should test them  A consumer should not access the private methods properties of your class  meaning you can change private members when the public exposed functionality stays the same     If you rely on internal extensible functionality  use protected instead of private  Note that protected is still a public API      just used differently   class OverlyComplicatedCalculator       public add    numbers  number     number           return this calculate  a  b    gt  a   b  numbers                can t be used or tested via   calculate     but it is still part of your public API      protected calculate operation  operands            let result   operands 0           for  let i   1  i  lt  operands length  operands                  result   operation result  operands i                      return result            Unit test protected properties in the same way a consumer would use them  via subclassing   it  should be extensible via calculate          gt        class TestCalculator extends OverlyComplicatedCalculator           public testWithArrays array  any     any                 const concat    a  b    gt     concat a  b                  tests the protected method             return this calculate concat  array                       let testCalc   new TestCalculator        let result   testCalc testWithArrays  1   two   3        expect result  toEqual  1   two   3

User · Answer

Do not write tests for private methods  This defeats the point of unit tests     You should be testing the public API of your class You should NOT be testing the implimentation details of your class   Example  class SomeClass      public addNumber a  number  b  number          return a   b          The test for this method should not need to change if later the implementation changes but the behaviour of the public API remains the same   class SomeClass      public addNumber a  number  b  number          return this add a  b          private add a  number  b  number           return a   b          Don t make methods and properties public just in order to test them  This usually means that either    You are trying to test implementation rather than API  public interface   You should move the logic in question into its own class to make testing easier

[angular] How to write unit testing for Angular / TypeScript for private methods with Jasmine

just use `// @ts-ignore`:

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