Go Unit Test irrelevant error "hostname resolving error" - postgresql

Question

I am trying to write unit test for this project
It appears that i need to refactor a lot and currently working on it. In order to test functions in project/api/handlers.go i was trying to write some unit test code however always taking error related with DB initializing. DB is from Psql Docker container. Error says given hostname is not valid, however without testing it works as no problem. Also, for Dockerized postgresql, container name is being used as hostname and this shouldn't be a problem.
The error is:
DB connection error: failed to connect to host=postgresdbT user=postgres database=worth2watchdb: hostname resolving error (lookup postgresdbT: no such host)
Process finished with the exit code 1
Anyway, i did a couple refactor and managed abstracting functions from DB query functions however this error still occurs and i cannot perform the test. So finally i decided to perform a totally blank test within same package simply checks with bcrypt package.
func TestCheckPasswordHash(t *testing.T) {
ret, err := HashPassword("password")
assert.Nil(t, err)
ok := CheckPasswordHash("password", ret)
if !ok {
t.Fail()
}
}
//HashPassword function hashes password with bcrypt algorithm as Cost value and return hashed string value with an error
func HashPassword(password string) (string, error) {
bytes, err := bcrypt.GenerateFromPassword([]byte(password), 4)
return string(bytes), err
}
//CheckPasswordHash function checks two inputs and returns TRUE if matches
func CheckPasswordHash(password, hash string) bool {
err := bcrypt.CompareHashAndPassword([]byte(hash), []byte(password))
return err == nil
}
However when I've tried to perform test for only TestCheckPasswordHash function with command of go test -run TestCheckPasswordHash ./api, it still gives same error. Btw, File is handlers_test.go, functions are at handlers.go file, package name is api for both .
There is no contact with any kind of DB related functions however i am having same error again and again. When i run this TestCheckPasswordHash code in another project or at project/util/util_test.go, it checks and passes as expected.
I don't know what to do, it seems that i cannot perform any test in this package unless figure this out.
Thanks in advance. Best wishes.

Answer 1

Was checking your repo, nice implementation, neat an simple good job!
I think your issue is in the init function, please try commenting it out and see if it work for that single test.
Is a bit complex to explain how the init function works without a graph of files as example but you can check the official documentation:
https://go.dev/doc/effective_go#init
PD: if this doesn't work please write me back

Answer 2

I've found the reason why this error occured and now it's solved.
This is partially related with Docker's working principle of how DB_Hostname must be declared but we can do nothing about it. So we need a better approach to overcome.
When go test command executed for (even) a function, Go testing logic checks whole package(not whole project) as per execution order, such as firstly variable declarations and init() function later. In case of calling an external package item, runtime detours that package for the item also.
Even if you are testing only an irrelevant function, you should consider that, before performing the test, Go runtime will evaluate whole package.
In order to prevent this, i wrapped the package level variables(even though they are in another package) that directly calls DB and cache. On initial stage, these can be allocated as a new variable. However, their connection will be ensured by main or main.init()
And now, prior to testing, all relevant variables (in same package or via external) are checked. Let's say if DB agent (redis.client or pgxpool.Pool) is needed, we are creating a new agent, compiler doesn't complain and testing begins. Agent will be operational only by a function call from main or somewhere we want to.
This is a better(may be not best) practice for a more maintainable code. Initialization of dependants should be able to be handled cautiously and in context with the functional needs. At least, with a simple refactoring, problem should be solvable.