My source files tree is like this:

/src
  /pkg
    /foo
      foo.go
      foo_test.go

Inside foo.go:

package foo

func bar(n int) {
    ...
}

inside foo_test.go:

package foo

func testBar(t *testing.T) {
    bar(10)
    ...
}

My questions are:

1. Does package name relates to directory name, source file name?
2. If there is only one source file for a package, need I put it in a directory?
3. Should I put foo.go and foo_test.go in the same package?
4. In the foo_test.go, as it's in the same package as foo.go, I didn't import foo. But when I compile foo_test.go with 6g, it says bar() is undefined. What should I do?