TDD/TDF with Golang

Abhishek Amralkar
3 min readNov 26, 2022
Photo by Chinmay Bhattar on Unsplash

The new style of writing a software is Test Driven Development or Test First Development and this isn’t only in Go. With this approach we first write the test or test-cases for a feature or enhancement, which made us think about the feature and its requirement precisely.

A new bank Foo-bar is incorporating and they decided to use Go for there application and to start with application will support 3 major operations

  • Balance
  • Credit
  • Debit

Lets write Credit function and some test cases for above Credit function. To create a project in Go create a directory say foobarbank and run command

go mod init

Above command will create go.modfile in the directory. Create file name *_test.go and Go will detect it .

  • Write your test in file name *_test.go.
  • Test function should always be named as Test* .
  • Test function only takes 1 argument t *testing.B .
  • To run a subtest we can use t.Run
  • We can use t.Helper() to deg=fine helper function
  • To run test run below command
go test

ok 0.001s


We can also check the coverage of our test cases

go test -cover

coverage: 25.0% of statements
ok 0.001s

Now time to write our `Credit` function which takes amount type int and add to Balance and return Balance as type int, that simple. func is the keyword in Go to create a function and as Go is statically type language you need to explicitly day what data type of argument a function except and what data type function will return if it return.

Though in this example we just writing test cases for 1 function which isnt true in the actual software. We can output a coverage report in .out format using go test

go test -coverprofile=coverage.out
coverage: 25.0% of statements
ok 0.002s

This will output a coverage.out file in pwd and we can use this report to see in html format using below command

go tool cover -html=coverage.out

This will open a tab in default browser and we can view the coverage as html


Benchmark are executed by the `go test` command when its -bench flag is provided. Benchmarks are run sequentially.

For a description of the testing flags, see

  • Benchmark function name should start from Benchmark
  • It takes exactly 1 parameter *testing.B
  • When Benchmark function executed, it runs b.N times and measures how long it takes.
  • By default Benchmarks are run sequentially.
  • We can pass -bench=. flag to test to run benchmark
go test -bench=.
goos: linux
goarch: amd64
cpu: Intel(R) Core(TM) i7-6500U CPU @ 2.50GHz
BenchmarkCredit-4 666403558 1.768 ns/op
ok 1.364s

Output 1.768 ns/op means is our benchmark function takes on average 1.768 nanoseconds to run . To test this it ran it 666403558 times. This results may defer from computer to computer and depends on the resources.

Helper Functions:

  • Helper functions accept a testing.TB which is an interface that *testing.T and *testing.B both satisfy.
  • Helper functions cab be called from a test, or a benchmark
  • t.Helper() is needed to tell the test suite that this method is a helper.