Unit testing is an important part of writing
principled Go programs. The
testing
package
provides the tools we need to write unit tests
and the
go test
command runs tests. | |
For the sake of demonstration, this code is in package
main
, but it could be any package. Testing code
typically lives in the same package as the code it tests. |  package main
|
| import (
"fmt"
"testing"
)
|
We’ll be testing this simple implementation of an
integer minimum. Typically, the code we’re testing
would be in a source file named something like
intutils.go
, and the test file for it would then
be named
intutils_test.go
. | func IntMin(a, b int) int {
if a < b {
return a
}
return b
}
|
A test is created by writing a function with a name
beginning with
Test
. | func TestIntMinBasic(t *testing.T) {
ans := IntMin(2, -2)
if ans != -2 {
|
t.Error*
will report test failures but continue
executing the test.
t.Fatal*
will report test
failures and stop the test immediately.
| t.Errorf("IntMin(2, -2) = %d; want -2", ans)
}
}
|
Writing tests can be repetitive, so it’s idiomatic to
use a
table-driven style
, where test inputs and
expected outputs are listed in a table and a single loop
walks over them and performs the test logic. | func TestIntMinTableDriven(t *testing.T) {
var tests = []struct {
a, b int
want int
}{
{0, 1, 0},
{1, 0, 0},
{2, -2, -2},
{0, -1, -1},
{-1, 0, -1},
}
|
t.Run enables running “subtests”, one for each
table entry. These are shown separately
when executing
go test -v
. | for _, tt := range tests {
|
| testname := fmt.Sprintf("%d,%d", tt.a, tt.b)
t.Run(testname, func(t *testing.T) {
ans := IntMin(tt.a, tt.b)
if ans != tt.want {
t.Errorf("got %d, want %d", ans, tt.want)
}
})
}
}
|
Benchmark tests typically go in
_test.go
files and are
named beginning with
Benchmark
. The
testing
runner
executes each benchmark function several times, increasing
b.N
on each run until it collects a precise measurement. | func BenchmarkIntMin(b *testing.B) {
|
Typically the benchmark runs a function we’re
benchmarking in a loop
b.N
times. | for i := 0; i < b.N; i++ {
IntMin(1, 2)
}
}
|