+This example package, numbers, consists of the function
+Double, which takes an int and returns that value
+multiplied by 2. It consists of three files.
+
+First, the package implementation, numbers.go:
+
+package numbers
+
+func Double(i int) int {
+ return i * 2
+}
+
+
+
+Next, the tests, numbers_test.go:
+
+package numbers
+
+import (
+ "testing"
+)
+
+type doubleTest struct {
+ in, out int
+}
+
+var doubleTests = []doubleTest{
+ doubleTest{1, 2},
+ doubleTest{2, 4},
+ doubleTest{-5, -10},
+}
+
+func TestDouble(t *testing.T) {
+ for _, dt := range doubleTests {
+ v := Double(dt.in)
+ if v != dt.out {
+ t.Errorf("Double(%d) returns %d; should be %d.", dt.in, v, dt.out)
+ }
+ }
+}
+
+
+
+Finally, the Makefile:
+
+include $(GOROOT)/src/Make.$(GOARCH) + +TARG=numbers +GOFILES=\ + numbers.go\ + +include $(GOROOT)/src/Make.pkg ++ +
+Running make install will build and install the package to
+the $GOROOT/pkg/ directory (it can then be used by any
+program on the system).
+
+Running make test (or just running the command
+gotest) will rebuild the package, including the
+numbers_test.go file, and then run the TestDouble
+function. The output "PASS" indicates that all tests passed
+successfully. Breaking the implementation by changing the multiplier from
+2 to 3 will allow you to see how failing tests are
+reported.
+
+See the gotest documentation and the +testing package for more detail. +