Add Docker checks (binary + daemon)

internal/check/docker.go

@@ -0,0 +1,37 @@
+package check
+
+import (
+	"context"
+	"os/exec"
+)
+
+type DockerDaemonCheck struct {
+	runner func() error
+}
+
+func (c *DockerDaemonCheck) Name() string {
+	return "Docker daemon running"
+}
+
+func (c *DockerDaemonCheck) Run(_ context.Context) Result {
+	run := c.runner
+	if run == nil {
+		run = func() error {
+			return exec.Command("docker", "info").Run()
+		}
+	}
+
+	if err := run(); err != nil {
+		return Result{
+			Name:    c.Name(),
+			Status:  StatusFail,
+			Message: "Docker daemon is not running",
+			Fix:     "start Docker and try again",
+		}
+	}
+	return Result{
+		Name:    c.Name(),
+		Status:  StatusPass,
+		Message: "Docker daemon is running",
+	}
+}

internal/check/docker_test.go

@@ -0,0 +1,23 @@
+package check
+
+import (
+	"context"
+	"errors"
+	"testing"
+)
+
+func TestDockerDaemonCheck_Pass(t *testing.T) {
+	c := &DockerDaemonCheck{runner: func() error { return nil }}
+	result := c.Run(context.Background())
+	if result.Status != StatusPass {
+		t.Errorf("expected pass, got %v: %s", result.Status, result.Message)
+	}
+}
+
+func TestDockerDaemonCheck_Fail(t *testing.T) {
+	c := &DockerDaemonCheck{runner: func() error { return errors.New("daemon not running") }}
+	result := c.Run(context.Background())
+	if result.Status != StatusFail {
+		t.Errorf("expected fail, got %v", result.Status)
+	}
+}

internal/check/registry.go

@@ -26,7 +26,8 @@ func Build(stack detector.DetectedStack) []Check {
 		}
 	}
 	if stack.Docker {
-		// add Docker checks
+		cs = append(cs, &BinaryCheck{Binary: "docker"})
+		cs = append(cs, &DockerDaemonCheck{})
 	}
 	if stack.Postgres {
 		// add Postgres checks