diff --git a/internal/buildfile/reader_test.go b/internal/buildfile/reader_test.go
index de71e4c..8c81e43 100644
--- a/internal/buildfile/reader_test.go
+++ b/internal/buildfile/reader_test.go
@@ -6,6 +6,27 @@ import (
 	"testing"
 )
 
+func TestNullContext(t *testing.T) {
+	buffer := bytes.NewBufferString("")
+	_, err := NewReader(nil, buffer)
+	if err != ErrNullContext {
+		t.Fatalf("expected <%s>, got <%v>", ErrNullContext, err)
+	}
+}
+func TestIgnoreCommentsAndEmptyLines(t *testing.T) {
+	ctx, _ := instruction.CreateContext("apt-get", "")
+	buffer := bytes.NewBufferString("[ some comment ]\n\n  \t  \n\t  \t\n[ other comment after empty lines ]")
+
+	r, err := NewReader(ctx, buffer)
+	if err != nil {
+		t.Fatalf("unexpected error <%v>", err)
+	}
+
+	if len(r.Content) > 0 {
+		t.Fatalf("expected no content, got %d instructions", len(r.Content))
+	}
+}
+
 func TestInstructionSyntax(t *testing.T) {
 	tests := []struct {
 		File string
diff --git a/internal/exec/common.go b/internal/exec/common.go
new file mode 100644
index 0000000..8c210ef
--- /dev/null
+++ b/internal/exec/common.go
@@ -0,0 +1,12 @@
+package exec
+
+// Command is the common interface wrapping os/exec.Command() output
+type Command interface {
+	Run() error
+	Output() ([]byte, error)
+}
+
+// Executor is the common interface wrapping os/exec.Command()
+type Executor interface {
+	Command(string, ...string) Command
+}
diff --git a/internal/exec/os.go b/internal/exec/os.go
new file mode 100644
index 0000000..969385a
--- /dev/null
+++ b/internal/exec/os.go
@@ -0,0 +1,11 @@
+package exec
+
+import (
+	osexec "os/exec"
+)
+
+type Default struct{}
+
+func (d *Default) Command(cmd string, args ...string) Command {
+	return osexec.Command(cmd, args...)
+}
diff --git a/internal/instruction/common.go b/internal/instruction/common.go
index f0b6ccc..7106edd 100644
--- a/internal/instruction/common.go
+++ b/internal/instruction/common.go
@@ -2,6 +2,7 @@ package instruction
 
 import (
 	"fmt"
+	"git.xdrm.io/go/nix-amer/internal/exec"
 	"git.xdrm.io/go/nix-amer/internal/pkg"
 	"git.xdrm.io/go/nix-amer/internal/ser"
 )
@@ -16,8 +17,14 @@ type T interface {
 	Exec(ExecutionContext) ([]byte, error)
 }
 
+// Executor is the common interface to execute commands
+type Executor interface {
+	Execute(...string) error
+}
+
 // ExecutionContext contains system-specific drivers to manage the host
 type ExecutionContext struct {
+	ExecContext    Executor
 	PackageManager pkg.PackageManager
 	ServiceManager ser.ServiceManager
 }
@@ -42,12 +49,14 @@ func CreateContext(_pkg, _ser string) (*ExecutionContext, error) {
 		_ser = ser.DefaultManager
 	}
 
+	executor := new(exec.Default)
+
 	// 3. load managers
-	pkg, err := pkg.Load(_pkg)
+	pkg, err := pkg.Load(_pkg, executor)
 	if err != nil {
 		return nil, fmt.Errorf("package manager: %s", err)
 	}
-	ser, err := ser.Load(_ser)
+	ser, err := ser.Load(_ser, executor)
 	if err != nil {
 		return nil, fmt.Errorf("service manager: %s", err)
 	}
diff --git a/internal/pkg/apk.go b/internal/pkg/apk.go
index ea332e5..c622620 100644
--- a/internal/pkg/apk.go
+++ b/internal/pkg/apk.go
@@ -1,25 +1,27 @@
 package pkg
 
-import (
-	"os/exec"
-)
+import "git.xdrm.io/go/nix-amer/internal/exec"
 
-type apk struct{}
+type apk struct{ exec exec.Executor }
+
+func (d *apk) SetExecutor(_exec exec.Executor) {
+	d.exec = _exec
+}
 
 func (d apk) Name() string { return "apk" }
 
 func (d apk) Fetch() error {
-	return exec.Command(d.Name(), "update").Run()
+	return d.exec.Command(d.Name(), "update").Run()
 }
 
 func (d apk) Upgrade() error {
-	return exec.Command(d.Name(), "upgrade").Run()
+	return d.exec.Command(d.Name(), "upgrade").Run()
 }
 
 func (d apk) Install(_pkg string) error {
-	return exec.Command(d.Name(), "add", _pkg).Run()
+	return d.exec.Command(d.Name(), "add", _pkg).Run()
 }
 
 func (d apk) Remove(_pkg string) error {
-	return exec.Command(d.Name(), "del", _pkg).Run()
+	return d.exec.Command(d.Name(), "del", _pkg).Run()
 }
diff --git a/internal/pkg/apt.go b/internal/pkg/apt.go
index 2f161ba..358cb61 100644
--- a/internal/pkg/apt.go
+++ b/internal/pkg/apt.go
@@ -1,40 +1,44 @@
 package pkg
 
 import (
-	"os/exec"
+	"git.xdrm.io/go/nix-amer/internal/exec"
 )
 
-type aptGet struct{}
+type aptGet struct{ exec exec.Executor }
+
+func (d *aptGet) SetExecutor(_exec exec.Executor) {
+	d.exec = _exec
+}
 
 func (d aptGet) Name() string { return "apt-get" }
 
 func (d aptGet) Fetch() error {
-	err := exec.Command(d.Name(), "update").Run()
+	err := d.exec.Command(d.Name(), "update").Run()
 	return err
 }
 
 func (d aptGet) Upgrade() error {
-	err := exec.Command(d.Name(), "upgrade").Run()
+	err := d.exec.Command(d.Name(), "upgrade").Run()
 	if err != nil {
 		return err
 	}
 
-	err = exec.Command(d.Name(), "dist-upgrade").Run()
+	err = d.exec.Command(d.Name(), "dist-upgrade").Run()
 	if err != nil {
 		return err
 	}
 
-	exec.Command(d.Name(), "autoremove").Run()
+	d.exec.Command(d.Name(), "autoremove").Run()
 	return nil
 }
 
 func (d aptGet) Install(_pkg string) error {
-	err := exec.Command(d.Name(), "install", _pkg).Run()
+	err := d.exec.Command(d.Name(), "install", _pkg).Run()
 	return err
 }
 
 func (d aptGet) Remove(_pkg string) error {
-	err := exec.Command(d.Name(), "remove", _pkg).Run()
-	exec.Command(d.Name(), "autoremove").Run()
+	err := d.exec.Command(d.Name(), "remove", _pkg).Run()
+	d.exec.Command(d.Name(), "autoremove").Run()
 	return err
 }
diff --git a/internal/pkg/common.go b/internal/pkg/common.go
index 54c6b27..b0ac043 100644
--- a/internal/pkg/common.go
+++ b/internal/pkg/common.go
@@ -1,10 +1,16 @@
 package pkg
 
+import (
+	"git.xdrm.io/go/nix-amer/internal/exec"
+)
+
 // DefaultManager if not empty is the default package-manager to use when missing
 var DefaultManager = ""
 
 // PackageManager is the common interface for all package-manager drivers (e.g. `dpkg` for debian-based, `pacman` for arch)
 type PackageManager interface {
+	// SetExecContext sets the execution context, default is os/exec
+	SetExecutor(exec.Executor)
 	// Name of executable (to check if installed and for debug)
 	Name() string
 	// Fetch updates the package cache/databse
diff --git a/internal/pkg/dnf.go b/internal/pkg/dnf.go
index d2f2da3..62d58e5 100644
--- a/internal/pkg/dnf.go
+++ b/internal/pkg/dnf.go
@@ -1,10 +1,12 @@
 package pkg
 
-import (
-	"os/exec"
-)
+import "git.xdrm.io/go/nix-amer/internal/exec"
 
-type dnf struct{}
+type dnf struct{ exec exec.Executor }
+
+func (d *dnf) SetExecutor(_exec exec.Executor) {
+	d.exec = _exec
+}
 
 func (d dnf) Name() string { return "dnf" }
 
@@ -13,17 +15,17 @@ func (d dnf) Fetch() error {
 }
 
 func (d dnf) Upgrade() error {
-	err := exec.Command(d.Name(), "upgrade").Run()
-	exec.Command(d.Name(), "autoremove").Run()
+	err := d.exec.Command(d.Name(), "upgrade").Run()
+	d.exec.Command(d.Name(), "autoremove").Run()
 	return err
 }
 
 func (d dnf) Install(_pkg string) error {
-	return exec.Command(d.Name(), "install", _pkg).Run()
+	return d.exec.Command(d.Name(), "install", _pkg).Run()
 }
 
 func (d dnf) Remove(_pkg string) error {
-	err := exec.Command(d.Name(), "remove", _pkg).Run()
-	exec.Command(d.Name(), "autoremove").Run()
+	err := d.exec.Command(d.Name(), "remove", _pkg).Run()
+	d.exec.Command(d.Name(), "autoremove").Run()
 	return err
 }
diff --git a/internal/pkg/eopkg.go b/internal/pkg/eopkg.go
index 5be6bc6..d4a311a 100644
--- a/internal/pkg/eopkg.go
+++ b/internal/pkg/eopkg.go
@@ -1,10 +1,12 @@
 package pkg
 
-import (
-	"os/exec"
-)
+import "git.xdrm.io/go/nix-amer/internal/exec"
 
-type eopkg struct{}
+type eopkg struct{ exec exec.Executor }
+
+func (d *eopkg) SetExecutor(_exec exec.Executor) {
+	d.exec = _exec
+}
 
 func (d eopkg) Name() string { return "eopkg" }
 
@@ -13,18 +15,18 @@ func (d eopkg) Fetch() error {
 }
 
 func (d eopkg) Upgrade() error {
-	err := exec.Command(d.Name(), "upgrade").Run()
-	exec.Command(d.Name(), "remove-orphans").Run()
+	err := d.exec.Command(d.Name(), "upgrade").Run()
+	d.exec.Command(d.Name(), "remove-orphans").Run()
 	return err
 }
 
 func (d eopkg) Install(_pkg string) error {
-	err := exec.Command(d.Name(), "install", _pkg).Run()
+	err := d.exec.Command(d.Name(), "install", _pkg).Run()
 	return err
 }
 
 func (d eopkg) Remove(_pkg string) error {
-	err := exec.Command(d.Name(), "remove", _pkg).Run()
-	exec.Command(d.Name(), "remove-orphans").Run()
+	err := d.exec.Command(d.Name(), "remove", _pkg).Run()
+	d.exec.Command(d.Name(), "remove-orphans").Run()
 	return err
 }
diff --git a/internal/pkg/loader.go b/internal/pkg/loader.go
index 63e8b26..1d08753 100644
--- a/internal/pkg/loader.go
+++ b/internal/pkg/loader.go
@@ -2,6 +2,7 @@ package pkg
 
 import (
 	"errors"
+	"git.xdrm.io/go/nix-amer/internal/exec"
 )
 
 // ErrUnknownManager is raised when the asked manager does not exist
@@ -13,7 +14,7 @@ var ErrUnknownManager = errors.New("unknown package manager")
 var ErrNotInstalled = errors.New("no candidate installed")
 
 // Load a specific package-manager by its name
-func Load(_manager string) (PackageManager, error) {
+func Load(_manager string, _exec exec.Executor) (PackageManager, error) {
 
 	// 1. create manager (fail if unknown)
 	var manager PackageManager
@@ -39,6 +40,7 @@ func Load(_manager string) (PackageManager, error) {
 	// 	return nil, ErrNotInstalled
 	// }
 
+	manager.SetExecutor(_exec)
 	return manager, nil
 
 }
diff --git a/internal/pkg/loader_test.go b/internal/pkg/loader_test.go
index 2c5fb82..9617810 100644
--- a/internal/pkg/loader_test.go
+++ b/internal/pkg/loader_test.go
@@ -1,12 +1,37 @@
 package pkg
 
 import (
+	"git.xdrm.io/go/nix-amer/internal/exec"
 	"testing"
 )
 
+/////////////////// MOCKUP START ///////////////////
+type MockupCommand struct {
+	Out []byte
+	Err error
+}
+
+func (c MockupCommand) Run() error              { return c.Err }
+func (c MockupCommand) Output() ([]byte, error) { return c.Out, c.Err }
+
+type MockupExecutor struct {
+	Out []byte
+	Err error
+}
+
+func (d MockupExecutor) Command(cmd string, args ...string) exec.Command {
+	return &MockupCommand{Out: d.Out, Err: d.Err}
+}
+
+/////////////////// MOCKUP END ///////////////////
+
 func TestUnknownManager(t *testing.T) {
 
-	_, err := Load("apt-put")
+	execctx := new(MockupExecutor)
+	execctx.Err = nil
+	execctx.Out = []byte{}
+
+	_, err := Load("apt-put", execctx)
 	if err != ErrUnknownManager {
 		t.Errorf("expected <%s>, got <%s>", ErrUnknownManager, err)
 		t.Fail()
@@ -14,8 +39,11 @@ func TestUnknownManager(t *testing.T) {
 
 }
 func TestKnownManager(t *testing.T) {
+	execctx := new(MockupExecutor)
+	execctx.Err = nil
+	execctx.Out = []byte{}
 
-	_, err := Load("apt-get")
+	_, err := Load("apt-get", execctx)
 	if err != nil {
 		t.Errorf("unexpected error <%s>", err)
 		t.Fail()
diff --git a/internal/pkg/pacman.go b/internal/pkg/pacman.go
index 304bf67..01f97e1 100644
--- a/internal/pkg/pacman.go
+++ b/internal/pkg/pacman.go
@@ -1,10 +1,12 @@
 package pkg
 
-import (
-	"os/exec"
-)
+import "git.xdrm.io/go/nix-amer/internal/exec"
 
-type pacman struct{}
+type pacman struct{ exec exec.Executor }
+
+func (d *pacman) SetExecutor(_exec exec.Executor) {
+	d.exec = _exec
+}
 
 func (d pacman) Name() string { return "pacman" }
 
@@ -13,18 +15,18 @@ func (d pacman) Fetch() error {
 }
 
 func (d pacman) Upgrade() error {
-	err := exec.Command(d.Name(), "-Syu").Run()
-	exec.Command(d.Name(), "-Ru").Run()
+	err := d.exec.Command(d.Name(), "-Syu").Run()
+	d.exec.Command(d.Name(), "-Ru").Run()
 	return err
 }
 
 func (d pacman) Install(_pkg string) error {
-	err := exec.Command(d.Name(), "-S", _pkg).Run()
+	err := d.exec.Command(d.Name(), "-S", _pkg).Run()
 	return err
 }
 
 func (d pacman) Remove(_pkg string) error {
-	err := exec.Command(d.Name(), "-R", _pkg).Run()
-	exec.Command(d.Name(), "-Ru").Run()
+	err := d.exec.Command(d.Name(), "-R", _pkg).Run()
+	d.exec.Command(d.Name(), "-Ru").Run()
 	return err
 }
diff --git a/internal/pkg/yum.go b/internal/pkg/yum.go
index 8c05779..8001fc6 100644
--- a/internal/pkg/yum.go
+++ b/internal/pkg/yum.go
@@ -1,10 +1,12 @@
 package pkg
 
-import (
-	"os/exec"
-)
+import "git.xdrm.io/go/nix-amer/internal/exec"
 
-type yum struct{}
+type yum struct{ exec exec.Executor }
+
+func (d *yum) SetExecutor(_exec exec.Executor) {
+	d.exec = _exec
+}
 
 func (d yum) Name() string { return "yum" }
 
@@ -13,13 +15,13 @@ func (d yum) Fetch() error {
 }
 
 func (d yum) Upgrade() error {
-	return exec.Command(d.Name(), "update").Run()
+	return d.exec.Command(d.Name(), "update").Run()
 }
 
 func (d yum) Install(_pkg string) error {
-	return exec.Command(d.Name(), "install", _pkg).Run()
+	return d.exec.Command(d.Name(), "install", _pkg).Run()
 }
 
 func (d yum) Remove(_pkg string) error {
-	return exec.Command(d.Name(), "remove", _pkg).Run()
+	return d.exec.Command(d.Name(), "remove", _pkg).Run()
 }
diff --git a/internal/ser/common.go b/internal/ser/common.go
index 5def149..23dbad9 100644
--- a/internal/ser/common.go
+++ b/internal/ser/common.go
@@ -1,10 +1,16 @@
 package ser
 
+import (
+	"git.xdrm.io/go/nix-amer/internal/exec"
+)
+
 // DefaultManager if not empty is the default service-manager to use when missing
 var DefaultManager = "systemd"
 
 // ServiceManager is the common interface for service managers (systemd, init.d)
 type ServiceManager interface {
+	// SetExecContext sets the execution context, default is os/exec
+	SetExecutor(exec.Executor)
 	// Name of executable (to check if installed and for debug)
 	Name() string
 	// Exec a specific action on a service
diff --git a/internal/ser/loader.go b/internal/ser/loader.go
index 99a15d7..9a7d261 100644
--- a/internal/ser/loader.go
+++ b/internal/ser/loader.go
@@ -2,6 +2,7 @@ package ser
 
 import (
 	"errors"
+	"git.xdrm.io/go/nix-amer/internal/exec"
 )
 
 // ErrUnknownManager is raised when the asked manager does not exist
@@ -13,7 +14,7 @@ var ErrUnknownManager = errors.New("unknown service manager")
 var ErrNotInstalled = errors.New("no candidate installed")
 
 // Load a specific service-manager by its name
-func Load(_manager string) (ServiceManager, error) {
+func Load(_manager string, _exec exec.Executor) (ServiceManager, error) {
 
 	// 1. create manager (fail if unknown)
 	var manager ServiceManager
@@ -29,6 +30,7 @@ func Load(_manager string) (ServiceManager, error) {
 	// 	return nil, ErrNotInstalled
 	// }
 
+	manager.SetExecutor(_exec)
 	return manager, nil
 
 }
diff --git a/internal/ser/systemd.go b/internal/ser/systemd.go
index c20ab04..feef320 100644
--- a/internal/ser/systemd.go
+++ b/internal/ser/systemd.go
@@ -1,14 +1,18 @@
 package ser
 
 import (
-	"os/exec"
+	"git.xdrm.io/go/nix-amer/internal/exec"
 )
 
-type systemd struct{}
+type systemd struct{ exec exec.Executor }
 
 // available actions
 var actions = []string{"enable", "disable", "start", "stop", "reload", "restart"}
 
+func (d *systemd) SetExecutor(_exec exec.Executor) {
+	d.exec = _exec
+}
+
 func (d systemd) Name() string { return "systemctl" }
 
 func (d systemd) Exec(action, service string) error {
@@ -26,6 +30,6 @@ func (d systemd) Exec(action, service string) error {
 	}
 
 	// 2. execute command
-	return exec.Command("systemctl", action, service).Run()
+	return d.exec.Command("systemctl", action, service).Run()
 
 }