How do you print in a Go test using the testing package

Question

I m running a test in Go with a statement to print something  i e  for debugging of tests  but it s not printing anything   func TestPrintSomething t  testing T        fmt Println  Say hi       When I run go test on this file  this is the output   ok      command-line-arguments  0 004s   The only way to really get it to print  as far as I know  is to print it via t Error    like so    func TestPrintSomethingAgain t  testing T        t Error  Say hi       Which outputs this   Say hi --- FAIL  TestPrintSomethingAgain  0 00 seconds      foo test go 35  Say hi FAIL FAIL    command-line-arguments  0 003s gom   exit status 1   I ve Googled and looked through the manual but didn t find anything

User · Accepted Answer

The structs testing T and testing B both have a  Log and  Logf method that sound to be what you are looking for   Log and  Logf are similar to fmt Print and fmt Printf respectively   See more details here  http   golang org pkg testing  pkg-index  fmt X print statements do work inside tests  but you will find their output is probably not on screen where you expect to find it and  hence  why you should use the logging methods in testing   If  as in your case  you want to see the logs for tests that are not failing  you have to provide go test the -v flag  v for verbosity   More details on testing flags can be found here  https   golang org cmd go  hdr-Testing flags

User · Answer

t Log and t Logf do print out in your test but can often be missed as it prints on the same line as your test  What I do is Log them in a way that makes them stand out  ie  t Run  FindIntercomUserAndReturnID should find an intercom user   func t  testing T         id  err    ic FindIntercomUserAndReturnID  test3 test com       assert Nil t  err      assert NotNil t  id       t Logf   n nid   v n n    id       which prints it to the terminal as       RUN   TestIntercom     RUN   TestIntercom FindIntercomUserAndReturnID should find an intercom user     TestIntercom FindIntercomUserAndReturnID should find an intercom user  intercom test go 34           id  5ea8caed05a4862c0d712008  --- PASS  TestIntercom  1 45s      --- PASS  TestIntercom FindIntercomUserAndReturnID should find an intercom user  1 45s  PASS ok      github com RuNpiXelruN third-party-delete-service   1 470s

User · Answer

In case your using testing M and associated setup teardown  -v is valid here as well  package g   import        quot os quot       quot fmt quot       quot testing quot     func TestSomething t  testing T        t Skip  quot later quot      func setup         fmt Println  quot setting up quot      func teardown         fmt Println  quot tearing down quot      func TestMain m  testing M        setup       result    m Run       teardown       os Exit result       go test -v g test go  setting up     RUN   TestSomething     g test go 10  later --- SKIP  TestSomething  0 00s  PASS tearing down ok      command-line-arguments  0 002s

User · Answer

The   test go file is a Go source like the others  you can initialize a new logger every time if you need to dump complex data structure  here an example      initZapLog is delegated to initialize a new  log manager  func initZapLog    zap Logger       config    zap NewDevelopmentConfig       config EncoderConfig EncodeLevel   zapcore CapitalColorLevelEncoder     config EncoderConfig TimeKey    timestamp      config EncoderConfig EncodeTime   zapcore ISO8601TimeEncoder     logger       config Build       return logger     Then  every time  in every test   func TestCreateDB t  testing T        loggerMgr    initZapLog          Make logger avaible everywhere     zap ReplaceGlobals loggerMgr      defer loggerMgr Sync      flushes buffer  if any     logger    loggerMgr Sugar       logger Debug  START       conf    initConf          Your test here     if false           t Fail

User · Answer

t Log   will not show up until after the test is complete  so if you re trying to debug a test that is hanging or performing badly it seems you need to use fmt    Yes  that was the case up to Go 1 13  August 2019  included   And that was followed in golang org issue 24929     Consider the following  silly  automated tests   func TestFoo t  testing T        t Parallel      for i    0  i  lt  15  i             t Logf   d   i          time Sleep 3   time Second           func TestBar t  testing T        t Parallel      for i    0  i  lt  15  i             t Logf   d   i          time Sleep 2   time Second           func TestBaz t  testing T        t Parallel      for i    0  i  lt  15  i             t Logf   d   i          time Sleep 1   time Second                If I run go test -v  I get no log output until all of TestFoo is done  then no output until all of TestBar is done  and again no more output until all of TestBaz is done    This is fine if the tests are working  but if there is some sort of bug  there are a few cases where buffering log output is problematic          When iterating locally  I want to be able to make a change  run my tests  see what s happening in the logs immediately to understand what s going on  hit CTRL C to shut the test down early if necessary  make another change  re-run the tests  and so on    If TestFoo is slow  e g   it s an integration test   I get no log output until the very end of the test  This significantly slows down iteration    If TestFoo has a bug that causes it to hang and never complete  I d get no log output whatsoever  In these cases  t Log and t Logf are of no use at all    This makes debugging very difficult    Moreover  not only do I get no log output  but if the test hangs too long  either the Go test timeout kills the test after 10 minutes  or if I increase that timeout  many CI servers will also kill off tests if there is no log output after a certain amount of time  e g   10 minutes in CircleCI     So now my tests are killed and I have nothing in the logs to tell me what happened       But for  possibly  Go 1 14  Q1 2020   CL 127120     testing  stream log output in verbose mode   The output now is       RUN   TestFoo     PAUSE TestFoo     RUN   TestBar     PAUSE TestBar     RUN   TestGaz     PAUSE TestGaz     CONT  TestFoo     TestFoo  main test go 14  hello from foo     CONT  TestGaz     CONT  TestBar     TestGaz  main test go 38  hello from gaz     TestBar  main test go 26  hello from bar     TestFoo  main test go 14  hello from foo     TestBar  main test go 26  hello from bar     TestGaz  main test go 38  hello from gaz     TestFoo  main test go 14  hello from foo     TestGaz  main test go 38  hello from gaz     TestBar  main test go 26  hello from bar     TestFoo  main test go 14  hello from foo     TestGaz  main test go 38  hello from gaz     TestBar  main test go 26  hello from bar     TestGaz  main test go 38  hello from gaz     TestFoo  main test go 14  hello from foo     TestBar  main test go 26  hello from bar --- PASS  TestFoo  1 00s  --- PASS  TestGaz  1 00s  --- PASS  TestBar  1 00s  PASS ok      dummy streaming-test    1 022s     It is indeed in Go 1 14  as Dave Cheney attests in  go test -v streaming output       In Go 1 14  go test -v will stream t Log output as it happens  rather than hoarding it til the end of the test run       Under Go 1 14 the fmt Println and t Log lines are interleaved  rather than waiting for the test to complete  demonstrating that test output is streamed when go test -v is used    Advantage  according to Dave      This is a great quality of life improvement for integration style tests that often retry for long periods when the test is failing    Streaming t Log output will help Gophers debug those test failures without having to wait until the entire test times out to receive their output

User · Answer

For example   package verbose  import        fmt       testing     func TestPrintSomething t  testing T        fmt Println  Say hi       t Log  Say bye         go test -v     RUN TestPrintSomething Say hi --- PASS  TestPrintSomething  0 00 seconds      v test go 10  Say bye PASS ok      so v    0 002s        Command go      Description of testing flags  -v Verbose output  log all tests as they are run  Also print all text from Log and Logf calls even if the test succeeds          Package testing      func   T  Log  func  c  T  Log args    interface          Log formats its arguments using default formatting  analogous to Println  and records the text in the error log  For tests  the text will be printed only if the test fails or the -test v flag is set  For benchmarks  the text is always printed to avoid having performance depend on the value of the -test v flag

User · Answer

For testing sometimes I do  fmt Fprintln os Stdout   hello     Also  you can print to   fmt Fprintln os Stderr   hello

[testing] How do you print in a Go test using the "testing" package?

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