diff --git a/internal/monitoring/metrics_helpers_test.go b/internal/monitoring/metrics_helpers_test.go
new file mode 100644
index 0000000..7012cd4
--- /dev/null
+++ b/internal/monitoring/metrics_helpers_test.go
@@ -0,0 +1,371 @@
+package monitoring
+
+import "testing"
+
+func TestNormalizeLabel(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  string
+	}{
+		{
+			name:  "normal string",
+			input: "proxmox",
+			want:  "proxmox",
+		},
+		{
+			name:  "empty string",
+			input: "",
+			want:  "unknown",
+		},
+		{
+			name:  "whitespace only",
+			input: "   ",
+			want:  "unknown",
+		},
+		{
+			name:  "leading whitespace",
+			input: "  docker",
+			want:  "docker",
+		},
+		{
+			name:  "trailing whitespace",
+			input: "docker  ",
+			want:  "docker",
+		},
+		{
+			name:  "both sides whitespace",
+			input: "  docker  ",
+			want:  "docker",
+		},
+		{
+			name:  "tabs",
+			input: "\ttab\t",
+			want:  "tab",
+		},
+		{
+			name:  "mixed whitespace",
+			input: " \t mixed \t ",
+			want:  "mixed",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := normalizeLabel(tt.input)
+			if got != tt.want {
+				t.Errorf("normalizeLabel(%q) = %q, want %q", tt.input, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestNormalizeNodeLabel(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  string
+	}{
+		{
+			name:  "normal node name",
+			input: "node1",
+			want:  "node1",
+		},
+		{
+			name:  "empty becomes unknown-node",
+			input: "",
+			want:  "unknown-node",
+		},
+		{
+			name:  "whitespace becomes unknown-node",
+			input: "   ",
+			want:  "unknown-node",
+		},
+		{
+			name:  "with whitespace trimmed",
+			input: "  pve-node2  ",
+			want:  "pve-node2",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := normalizeNodeLabel(tt.input)
+			if got != tt.want {
+				t.Errorf("normalizeNodeLabel(%q) = %q, want %q", tt.input, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestSplitInstanceKey(t *testing.T) {
+	tests := []struct {
+		name         string
+		key          string
+		wantType     string
+		wantInstance string
+	}{
+		{
+			name:         "normal key",
+			key:          "proxmox::server1",
+			wantType:     "proxmox",
+			wantInstance: "server1",
+		},
+		{
+			name:         "docker key",
+			key:          "docker::prod-docker",
+			wantType:     "docker",
+			wantInstance: "prod-docker",
+		},
+		{
+			name:         "empty key",
+			key:          "",
+			wantType:     "unknown",
+			wantInstance: "unknown",
+		},
+		{
+			name:         "no separator",
+			key:          "standalone",
+			wantType:     "unknown",
+			wantInstance: "standalone",
+		},
+		{
+			name:         "multiple separators",
+			key:          "type::instance::extra",
+			wantType:     "type",
+			wantInstance: "instance::extra",
+		},
+		{
+			name:         "empty type",
+			key:          "::instance",
+			wantType:     "unknown",
+			wantInstance: "instance",
+		},
+		{
+			name:         "empty instance",
+			key:          "type::",
+			wantType:     "type",
+			wantInstance: "unknown",
+		},
+		{
+			name:         "whitespace in parts",
+			key:          " proxmox :: server1 ",
+			wantType:     "proxmox",
+			wantInstance: "server1",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotType, gotInstance := splitInstanceKey(tt.key)
+			if gotType != tt.wantType || gotInstance != tt.wantInstance {
+				t.Errorf("splitInstanceKey(%q) = (%q, %q), want (%q, %q)",
+					tt.key, gotType, gotInstance, tt.wantType, tt.wantInstance)
+			}
+		})
+	}
+}
+
+func TestBreakerStateToValue(t *testing.T) {
+	tests := []struct {
+		name  string
+		state string
+		want  float64
+	}{
+		{
+			name:  "closed",
+			state: "closed",
+			want:  0,
+		},
+		{
+			name:  "closed uppercase",
+			state: "CLOSED",
+			want:  0,
+		},
+		{
+			name:  "closed mixed case",
+			state: "Closed",
+			want:  0,
+		},
+		{
+			name:  "half_open underscore",
+			state: "half_open",
+			want:  1,
+		},
+		{
+			name:  "half-open hyphen",
+			state: "half-open",
+			want:  1,
+		},
+		{
+			name:  "half_open uppercase",
+			state: "HALF_OPEN",
+			want:  1,
+		},
+		{
+			name:  "open",
+			state: "open",
+			want:  2,
+		},
+		{
+			name:  "open uppercase",
+			state: "OPEN",
+			want:  2,
+		},
+		{
+			name:  "unknown state",
+			state: "invalid",
+			want:  -1,
+		},
+		{
+			name:  "empty string",
+			state: "",
+			want:  -1,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := breakerStateToValue(tt.state)
+			if got != tt.want {
+				t.Errorf("breakerStateToValue(%q) = %v, want %v", tt.state, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestSanitizeInstanceLabels(t *testing.T) {
+	tests := []struct {
+		name         string
+		instanceType string
+		instance     string
+		wantType     string
+		wantInstance string
+	}{
+		{
+			name:         "normal values",
+			instanceType: "proxmox",
+			instance:     "server1",
+			wantType:     "proxmox",
+			wantInstance: "server1",
+		},
+		{
+			name:         "empty type",
+			instanceType: "",
+			instance:     "server1",
+			wantType:     "unknown",
+			wantInstance: "server1",
+		},
+		{
+			name:         "empty instance",
+			instanceType: "docker",
+			instance:     "",
+			wantType:     "docker",
+			wantInstance: "unknown",
+		},
+		{
+			name:         "both empty",
+			instanceType: "",
+			instance:     "",
+			wantType:     "unknown",
+			wantInstance: "unknown",
+		},
+		{
+			name:         "whitespace trimmed",
+			instanceType: "  docker  ",
+			instance:     "  prod  ",
+			wantType:     "docker",
+			wantInstance: "prod",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotType, gotInstance := sanitizeInstanceLabels(tt.instanceType, tt.instance)
+			if gotType != tt.wantType || gotInstance != tt.wantInstance {
+				t.Errorf("sanitizeInstanceLabels(%q, %q) = (%q, %q), want (%q, %q)",
+					tt.instanceType, tt.instance, gotType, gotInstance, tt.wantType, tt.wantInstance)
+			}
+		})
+	}
+}
+
+func TestMakeMetricKey(t *testing.T) {
+	tests := []struct {
+		name         string
+		instanceType string
+		instance     string
+		wantKey      metricKey
+	}{
+		{
+			name:         "normal values",
+			instanceType: "proxmox",
+			instance:     "server1",
+			wantKey:      metricKey{instanceType: "proxmox", instance: "server1"},
+		},
+		{
+			name:         "empty values become unknown",
+			instanceType: "",
+			instance:     "",
+			wantKey:      metricKey{instanceType: "unknown", instance: "unknown"},
+		},
+		{
+			name:         "whitespace trimmed",
+			instanceType: "  docker  ",
+			instance:     "  prod  ",
+			wantKey:      metricKey{instanceType: "docker", instance: "prod"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := makeMetricKey(tt.instanceType, tt.instance)
+			if got != tt.wantKey {
+				t.Errorf("makeMetricKey(%q, %q) = %+v, want %+v",
+					tt.instanceType, tt.instance, got, tt.wantKey)
+			}
+		})
+	}
+}
+
+func TestMakeNodeMetricKey(t *testing.T) {
+	tests := []struct {
+		name         string
+		instanceType string
+		instance     string
+		node         string
+		wantKey      nodeMetricKey
+	}{
+		{
+			name:         "normal values",
+			instanceType: "proxmox",
+			instance:     "server1",
+			node:         "node1",
+			wantKey:      nodeMetricKey{instanceType: "proxmox", instance: "server1", node: "node1"},
+		},
+		{
+			name:         "empty node becomes unknown",
+			instanceType: "proxmox",
+			instance:     "server1",
+			node:         "",
+			wantKey:      nodeMetricKey{instanceType: "proxmox", instance: "server1", node: "unknown"},
+		},
+		{
+			name:         "all empty",
+			instanceType: "",
+			instance:     "",
+			node:         "",
+			wantKey:      nodeMetricKey{instanceType: "unknown", instance: "unknown", node: "unknown"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := makeNodeMetricKey(tt.instanceType, tt.instance, tt.node)
+			if got != tt.wantKey {
+				t.Errorf("makeNodeMetricKey(%q, %q, %q) = %+v, want %+v",
+					tt.instanceType, tt.instance, tt.node, got, tt.wantKey)
+			}
+		})
+	}
+}