Go - Error when compiling a group of functions

I'm trying to implement a very simple test function to verify results coming from my solutions for Euler problems.

In the following code I've created a map of slices where on the index 0, I call the function which return a integer and on the index 1, the result I expect from that function.

package euler

import "testing"

func TestEulers(t *testing.T) {

	tests := map[string][]int{
		"Euler1": {Euler1(), 233168},
		"Euler2": {Euler2(), 4613732},
		"Euler3": {Euler3(), 6857},
		"Euler4": {Euler4(), 906609},
		"Euler5": {Euler5(), 232792560},
		"Euler6": {Euler6(), 25164150},
	}

	for key, value := range tests {
		if value[0] != value[1] {
			t.Errorf("%s\nExpected: %d\nGot:%d",
				key, value[0], value[1])
		}
	}
}

For that map, every function works fine and return the result I expect if I run one by one or if I comment, let's say, half part of those keys/values.

For example, if I call the the function above with these lines commented the test will PASS.

tests := map[string][]int{
	"Euler1": {Euler1(), 233168},
	// "Euler2": {Euler2(), 4613732},
	"Euler3": {Euler3(), 6857},
	"Euler4": {Euler4(), 906609},
	// "Euler5": {Euler5(), 232792560},
	// "Euler6": {Euler6(), 25164150},
} 

But if I arrange the comments on that next way, for example, the test wouldn't.

tests := map[string][]int{
		//"Euler1": {Euler1(), 233168},
		"Euler2": {Euler2(), 4613732},
		"Euler3": {Euler3(), 6857},
		"Euler4": {Euler4(), 906609},
		//"Euler5": {Euler5(), 232792560},
		// "Euler6": {Euler6(), 25164150},
	}

The test will give me an error:

    WARNING: DATA RACE
Write by goroutine 6:
  runtime.closechan()
      /private/var/folders/q8/bf_4b1ts2zj0l7b0p1dv36lr0000gp/T/workdir/go/src/runtime/chan.go:295 +0x0
  github.com/alesr/project-euler.Euler2()
      /Users/Alessandro/GO/src/github.com/alesr/project-euler/euler.go:40 +0xd7
  github.com/alesr/project-euler.TestEulers()
      /Users/Alessandro/GO/src/github.com/alesr/project-euler/euler_test.go:9 +0x46
  testing.tRunner()
      /private/var/folders/q8/bf_4b1ts2zj0l7b0p1dv36lr0000gp/T/workdir/go/src/testing/testing.go:456 +0xdc

Previous read by goroutine 7:
  runtime.chansend()
      /private/var/folders/q8/bf_4b1ts2zj0l7b0p1dv36lr0000gp/T/workdir/go/src/runtime/chan.go:107 +0x0
  github.com/alesr/numbers.FibonacciGen.func1()
      /Users/Alessandro/GO/src/github.com/alesr/numbers/numbers.go:103 +0x59

Goroutine 6 (running) created at:
  testing.RunTests()
      /private/var/folders/q8/bf_4b1ts2zj0l7b0p1dv36lr0000gp/T/workdir/go/src/testing/testing.go:561 +0xaa3
  testing.(*M).Run()
      /private/var/folders/q8/bf_4b1ts2zj0l7b0p1dv36lr0000gp/T/workdir/go/src/testing/testing.go:494 +0xe4
  main.main()
      github.com/alesr/project-euler/_test/_testmain.go:54 +0x20f

Goroutine 7 (running) created at:
  github.com/alesr/numbers.FibonacciGen()
      /Users/Alessandro/GO/src/github.com/alesr/numbers/numbers.go:105 +0x60
  github.com/alesr/project-euler.Euler2()
      /Users/Alessandro/GO/src/github.com/alesr/project-euler/euler.go:27 +0x32
  github.com/alesr/project-euler.TestEulers()
      /Users/Alessandro/GO/src/github.com/alesr/project-euler/euler_test.go:9 +0x46
  testing.tRunner()
      /private/var/folders/q8/bf_4b1ts2zj0l7b0p1dv36lr0000gp/T/workdir/go/src/testing/testing.go:456 +0xdc
==================
panic: send on closed channel

goroutine 36 [running]:
github.com/alesr/numbers.FibonacciGen.func1(0xc8200a01e0)
	/Users/Alessandro/GO/src/github.com/alesr/numbers/numbers.go:103 +0x5a
created by github.com/alesr/numbers.FibonacciGen
	/Users/Alessandro/GO/src/github.com/alesr/numbers/numbers.go:105 +0x61

goroutine 1 [chan receive]:
testing.RunTests(0x24d038, 0x2f7340, 0x1, 0x1, 0xf78401)
	/private/var/folders/q8/bf_4b1ts2zj0l7b0p1dv36lr0000gp/T/workdir/go/src/testing/testing.go:562 +0xafa
testing.(*M).Run(0xc82004df00, 0x1ff0e8)
	/private/var/folders/q8/bf_4b1ts2zj0l7b0p1dv36lr0000gp/T/workdir/go/src/testing/testing.go:494 +0xe5
main.main()
	github.com/alesr/project-euler/_test/_testmain.go:54 +0x210

goroutine 17 [syscall, locked to thread]:
runtime.goexit()
	/private/var/folders/q8/bf_4b1ts2zj0l7b0p1dv36lr0000gp/T/workdir/go/src/runtime/asm_amd64.s:1696 +0x1

goroutine 35 [runnable]:
github.com/alesr/strings.Flip(0xc8200727a0, 0x6, 0x0, 0x0)
	/Users/Alessandro/GO/src/github.com/alesr/strings/strings.go:33 +0x17e
github.com/alesr/project-euler.Euler4(0x1ac9)
	/Users/Alessandro/GO/src/github.com/alesr/project-euler/euler.go:73 +0x95
github.com/alesr/project-euler.TestEulers(0xc8200b6000)
	/Users/Alessandro/GO/src/github.com/alesr/project-euler/euler_test.go:11 +0x63
testing.tRunner(0xc8200b6000, 0x2f7340)
	/private/var/folders/q8/bf_4b1ts2zj0l7b0p1dv36lr0000gp/T/workdir/go/src/testing/testing.go:456 +0xdd
created by testing.RunTests
	/private/var/folders/q8/bf_4b1ts2zj0l7b0p1dv36lr0000gp/T/workdir/go/src/testing/testing.go:561 +0xaa4
exit status 2
FAIL	github.com/alesr/project-euler	0.022s

But still, I checked every single function and they work just as expected.
You can access the Euler source code or the packages numbers and strings if you want.

At Euler2 function I have a defer statement to close the channel which is receiving from FibonacciGen.

And on FibonacciGen I do have another defer statement to close the same channel.

It seems that's the my first error. I should have just one and not two statements to close the channel, since they are trying to close the same thing. Is that correct?

Second (and here I'm even a little more unsure), the defer statement will prevent the function to be called until the main goroutine returns, right? Independently if I call it on the package main or not?

Plus, since the data is flowing through the channel from FibonacciGen to the main function. It seems for me, that if I close the channel at FibonacciGen I don't need to notify the main function. But If I close the channel on the main function I do have to notify FibonacciGen to stop trying to send to this channel.

In your Euler2() you don't check if the channel has been closed. Once it's closed it's unblocked, so it tries to send a value to a now closed channel.

If you only run Euler2() your program might just exit before you send the value to the closed channel.

Thank you all. With your help I could understand that I was closing the channel in the wrong way.

Now works correctly.

func Euler2() int {

	c := make(chan int)
	done := make(chan bool)

	go numbers.FibonacciGen(c, done)

	sum := 0
	var f int

	for {
		f = <-c
		if f < 4000000 {
			if f%2 == 0 {
				sum += f
			}
		} else {
			close(done)
			return sum
		}
	}
}

func FibonacciGen(c chan int, done chan bool) {

	for {
		select {
		case <-done:
			return
		default:
			for i, j := 0, 1; ; i, j = i+j, i {
				c <- i
			}
		}
	}

}