Go test <function> returns undefined: <function>

Question

Trying to run "go test sum_test.go" returns an error:

./sum_test.go:18:13: undefined: SumInt8 FAIL command-line-arguments [build failed]

I'm taking an introductory course in golang. Our teacher distributed a code-file, sum.go, and a testing-file, sum_test.go. Trying to run "go test" on sum_test.go returns the error above. The code runs fine on our teachers mac, and he's having difficulties recreating the problem. Here's my go environment settings: https://pastebin.com/HcuNVcAF

sum.go

package sum

func SumInt8(a, b int8) int8 {
  return a + b
}

func SumFloat64(a, b float64) float64 {
  return a + b
}

sum_test.go

package sum

import "testing"

// Check https://golang.org/ref/spec#Numeric_types and stress the limits!
var sum_tests_int8 = []struct{
  n1       int8
  n2       int8
  expected int8
}{
  {1, 2, 3},
  {4, 5, 9},
  {120, 1, 121},
}

func TestSumInt8(t *testing.T) {
for _, v := range sum_tests_int8 {
    if val := SumInt8(v.n1, v.n2); val != v.expected {
        t.Errorf("Sum(%d, %d) returned %d, expected %d", 
v.n1, v.n2, val, v.expected)
    }
  }
}

I see no particular errors, so I expected "go test sum_test.go" to run, and succeed. However it seems it can't find the method SumInt8 in sum.go.

Answer 1

$ go help packages

Many commands apply to a set of packages:

go action [packages]

Usually, [packages] is a list of import paths.

An import path that is a rooted path or that begins with a . or .. element is interpreted as a file system path and denotes the package in that directory.

Otherwise, the import path P denotes the package found in the directory DIR/src/P for some DIR listed in the GOPATH environment variable (For more details see: 'go help gopath').

If no import paths are given, the action applies to the package in the current directory.

As a special case, if the package list is a list of .go files from a single directory, the command is applied to a single synthesized package made up of exactly those files, ignoring any build constraints in those files and ignoring any other files in the directory.

---

List all the files in the current directory used in the test:

go test sum_test.go sum.go

or simply test the complete package in the current directory.

go test

---

For example,

$ go test -v sum_test.go sum.go
=== RUN   TestSumInt8
--- PASS: TestSumInt8 (0.00s)
PASS
ok      command-line-arguments  0.002s
$ 

or, for the complete package

$ go test -v
=== RUN   TestSumInt8
--- PASS: TestSumInt8 (0.00s)
PASS
ok      so/sum  0.002s
$

Option '-v' produces verbose output.

sum_test.go:

package sum

import "testing"

// Check https://golang.org/ref/spec#Numeric_types and stress the limits!
var sum_tests_int8 = []struct {
    n1       int8
    n2       int8
    expected int8
}{
    {1, 2, 3},
    {4, 5, 9},
    {120, 1, 121},
}

func TestSumInt8(t *testing.T) {
    for _, v := range sum_tests_int8 {
        if val := SumInt8(v.n1, v.n2); val != v.expected {
            t.Errorf("Sum(%d, %d) returned %d, expected %d",
                v.n1, v.n2, val, v.expected)
        }
    }
}

sum.go:

package sum

func SumInt8(a, b int8) int8 {
    return a + b
}

func SumFloat64(a, b float64) float64 {
    return a + b
}

---