fix(tests): cleanup Docker volumes in smoke tests

Add explicit Docker volume cleanup to prevent disk space
exhaustion in CI environments. Registry containers create
persistent volumes that were not being removed, causing
"No space left on device" errors in GitHub Actions.

Changes:
- Enhanced TestRegistry.Close() to inspect and remove
  associated volumes before container deletion
- Added CleanupDockerVolumes() helper method to prune
  unused volumes across all tests
- Updated all smoke tests (airgap, hello, desiredstate)
  to call volume cleanup in defer blocks

The registry:2 image stores data in /var/lib/registry
which creates Docker volumes. With multiple registries
per test (airgap test creates 12), these volumes were
accumulating and filling disk space.

Signed-off-by: Kim Christensen <kimworking@gmail.com>

Author: kichristensen

tests/smoke/airgap_test.go

@@ -55,6 +55,7 @@ func TestAirgappedEnvironment(t *testing.T) {
 			defer func() {
 				test.CleanupBundleImages("mybuns")
 				test.CleanupDanglingImages()
+				test.CleanupDockerVolumes()
 			}()
 
 			// Enable optimized build if requested

tests/smoke/desiredstate_test.go

@@ -45,6 +45,7 @@ func runDesiredStateTest(t *testing.T, enableOptimizedBuild bool) {
 		test.CleanupBundleImages("mybuns")
 		test.CleanupBundleImages("mydb")
 		test.CleanupDanglingImages()
+		test.CleanupDockerVolumes()
 	}()
 
 	// Enable optimized build if requested

tests/smoke/hello_test.go

@@ -45,6 +45,7 @@ func runHelloBundleTest(t *testing.T, enableOptimizedBuild bool) {
 		test.CleanupBundleImages("mybuns")
 		test.CleanupBundleImages("mydb")
 		test.CleanupDanglingImages()
+		test.CleanupDockerVolumes()
 	}()
 
 	// Enable optimized build if requested

tests/tester/main.go

@@ -282,3 +282,15 @@ func (t Tester) CleanupDockerBuildCache() {
 		t.T.Logf("Warning: could not prune build cache: %v", err)
 	}
 }
+
+// CleanupDockerVolumes removes unused Docker volumes to free disk space.
+// This is an optional cleanup method that tests can call explicitly when disk space is a concern.
+func (t Tester) CleanupDockerVolumes() {
+	t.T.Helper()
+	t.T.Log("Cleaning up unused Docker volumes")
+
+	// Prune unused volumes
+	if err := shx.RunE("docker", "volume", "prune", "-f"); err != nil {
+		t.T.Logf("Warning: could not prune volumes: %v", err)
+	}
+}

tests/tester/test_registry.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -47,16 +48,31 @@ func (t *TestRegistry) String() string {
 	return fmt.Sprintf("%s:%s", t.hostname, t.port)
 }
 
-// Close stops the registry.
+// Close stops the registry and removes its volumes.
 func (t *TestRegistry) Close() {
 	// Only call close once
 	if t.closed {
 		return
 	}
 
+	// Remove the container and its associated volumes
+	// First get the volumes associated with this container
+	volumes, _ := shx.OutputE("docker", "inspect", "-f", "{{ range .Mounts }}{{ .Name }} {{ end }}", t.containerID)
+
+	// Remove the container
 	err := shx.RunE("docker", "rm", "-vf", t.containerID)
 	t.closed = true
 	assert.NoError(t.t, err)
+
+	// Clean up any volumes that were associated with the container
+	// The -v flag on docker rm doesn't always remove volumes, especially named ones
+	if volumes != "" {
+		for _, vol := range strings.Fields(volumes) {
+			if vol != "" {
+				shx.RunE("docker", "volume", "rm", vol)
+			}
+		}
+	}
 }
 
 // StartTestRegistry runs an OCI registry in a container,