refactor cli.Interface yet again

- Only one global instance now, so we don't need to pass it around all
  the time.

- Allow to swap out the Command.Run implementation for unit tests.

- Can now use cli.Interface during func init() of packages importing
  pkg/cli.

1 files changed, 8 insertions, 2 deletions

diff --git a/pkg/cli/command.go b/pkg/cli/command.go
index 5b3ded5..d07a120 100644
--- a/pkg/cli/command.go
+++ b/pkg/cli/command.go
@@ -26,7 +26,7 @@ import (
 )
 
 //Command describes a command that can be run using the methods in the
-//Interface interface.
+//Implementation interface.
 type Command struct {
 	Program []string
 	WorkDir string
@@ -49,8 +49,14 @@ func (e commandError) Error() string {
 	)
 }
 
-func (c Command) run(stdout, stderr io.Writer) error {
+//CommandRunner is a function that can execute commands given to it.
+//This interface is only useful for unit tests; the default CommandRunner
+//suffices for all regular operation.
+type CommandRunner func(c Command, stdin io.Reader, stdout, stderr io.Writer) error
+
+func DefaultCommandRunner(c Command, stdin io.Reader, stdout, stderr io.Writer) error {
 	cmd := exec.Command(c.Program[0], c.Program[1:]...)
+	cmd.Stdin = stdin
 	cmd.Stdout = stdout
 	cmd.Stderr = stderr
 	cmd.Dir = c.WorkDir