writing-tests.slide

Writing tests in Go
13 August 2016

Kaviraj Kanagaraj
Aircto ( A Product by Launchyard)
kaviraj@launchyard.com
https://kaviraj.me
@kvrajk

* Agenda

- Basics
- Understanding white-box and black-box testing
- Real-time problems in testing
- Writing Testable Code
- Testing tricky parts
- Conclusion
- Resources

* Basics

* Go built-in testing framework

Entire testing framework built on top of _two_ components.

- *go* *test* command

- *testing* package


* What go test tool  do?

- Scans the `*_test.go` files for special functions (functions that start with `Test`, `Benchmark` and  `Example`)
- Generates a temporary main package
- Builds and runs it
- Report the results
- And finally Cleans up.

* Types of test functions

- Common tests
    func TestCopyBuffer(t *testing.T) {...}
- Benchmark tests
  func BenchmarkTrimSpace(b *testing.B) {...}
- Example tests
  func ExampleTrimPrefix(){...}


* Simple Problem - Reverse a given string

.play -edit writing-tests/reverse/reverse.go 

* Common tests (1/3)

.code -edit writing-tests/reverse/reverse_test.go /^func TestReverse/,/^}/

* Common tests (2/3)

.code -edit writing-tests/reverse/reverse_test.go /^func TestReverseUnicode/,/^}/

* Common tests (3/3)

*testing.T*

- t.Error()
- t.Fatal()
- t.Skip()
- t.Parallel()

* Benchmark tests

- Used to measure the performance of a program on a fixed workload.
- By default no benchmark tests are run. include *-bench=.* to run all the benchmark tests in the package

.code writing-tests/reverse/reverse_test.go /^func Bench/,/^}/

To run:

	  $ go test -bench=.
	  $ go test -bench=. -benchmem



* Example tests

- Test functions that starts with `Example` will be treated specially by `go` `test`
- They neither have *parameters* nor *results*

.code writing-tests/reverse/reverse_test.go /^func Example/,/^}/

Three purposes

- Provides good documentation for the APIs
- Easy to maintain the documentation as code evolves (Example tests are real executable code that get executed on `go` `test`)
- Used by godoc server

* Coverage

- Testing is never complete
- `Coverage` increase the confidence that package works well in a wide range of important/critical scenarios
- `Statement` `Coverage`
- Use Go's `cover` `tool` to measure coverage report

To run:

   $ go test -cover                 // prints coverage report on stdout
   $ go test -coverprofile=fmt.out  // creates coverage profile for further analysis
   $ go tool cover -html=c.out      // To see HTML report of the generated coverage profile


*Demo* *on* *fmt* *package*!*
   

* Profiling (1/2)

Trying to identify critical code of the system to increase the performance?

Start with *Profiling*.

Helps in identifying and correcting the bottlenecks

Types

- *CPU* *profile* - Identifies the functions whose execution requires most CPU

- *Heap* *profile* - Identifies statements responsible for allocating the most memory

- *Blocking* *profile* - Identifies the operations responsible for blocking goroutines

* Profiling (2/2)

Use *go* *tool* *pprof* to analyse the profile report

To run:

   $ go test -cpuprofile=cpu.out
   $ go test -memprofile=mem.out
   $ go test -blockprofile=block.out


*DEMO* *on* *net/http* *package!*

* White-box and Black-box testing

* Examples from standard library

* Real problems in testing

Mocking, mocking, mocking!!

- Should not send actual emails
- Should not hit actual database
- etc..

* Writing Testable Code

* Why is it important?

You cannot mock everything at the runtime(like Django/python). Though it works for some cases, its not idiomatic way.

Writing code that can be easily tested is the idiomatic way.

*Two* *simple* *Problems*

- Reset User's password

- Send Notification Email

* Reset User's Password

* Reset User's Password (1/5)

.code writing-tests/resetpassword/resetpassword.go /^func main/,/^}/

* Reset User's Password (2/5)

*Testable* *version*

.code writing-tests/resetpassword/resetpassword_better.go /^func main/,/^}/

* Reset User's Password (3/5)

.code writing-tests/resetpassword/resetpassword_better.go /^func ResetPassword/,/^}/

.code writing-tests/resetpassword/resetpassword_better.go /START2/,/END2/


* Reset User's Password (4/5)

.code writing-tests/resetpassword/resetpassword_better.go /START1/,/END1/

* Reset User Password (5/5)

.code writing-tests/resetpassword/resetpassword_test.go /^func TestResetPassword/,/^}/

* Send Notification Email

* Send notification email

.code writing-tests/email/emails.go /^func SendInvitationEmail/,/^}/

.code writing-tests/email/emails.go /START1/,/END1/


* Send notification email

.code writing-tests/email/emails.go /START2/,/END2/

* Send notification email

*Testable* *Version*

.code writing-tests/email/emails_better.go /START/,/END/

* Send Notification Email

.code writing-tests/email/emails_better.go /START2/,/END2/

* Send Notification Email

.code writing-tests/email/emails_test.go /START1/,/END1/ 

* Send Notification Email

.code writing-tests/email/emails_test.go /START2/,/END2/

* Testing Tricky Parts

* Testing tricky parts (1/2)

Testing the functions that `Fatals` or `Exits` for some invalid inputs or behaviour

*Example*

.code writing-tests/tricky/tricky.go /^func mustEnv/,/^}/

Now, how do we test, whether *mustEnv(key)* exits if particular *key* is not set in environment variables?


* Testing tricky parts (2/2)

.code writing-tests/tricky/tricky_test.go /^func TestMustEnv/,/^}/


* Conclusion

*I'm* *not* *a* *great* *programmer;* *I'm* *just* *a* *good* *programmer* *with* *great* *habit* *-* *Kent* *Beck*

- Writing Tests is a great habit

- Makes the codebase evolve and maintanable

- Makes you a better Programmer!


* Reference

- [[https://www.youtube.com/watch?v=ndmB0bj7eyw][Testing Techniques]] talk by Andrew Gerrand
- Standard Library
- [[https://golang.org/pkg/testing/][testing]] package documentation
- go tool cover
- go tool pprof

*Books*

- *The* *Go* *programming* *launguage* by Alan A.A Donovan & Brian W. Kernighan (11th Chapter)
- *Web* *Development* *with* *Go* by Shiju Varghese (Covers basics of testing Web APIs)