Add unit tests for pulse-sensor-proxy utility functions

- hashIPToUID: 11 test cases covering IP hashing for rate limiting
  (determinism, range bounds, collision detection, boundary values)
- extractNodesFromYAML: 17 test cases covering YAML node list parsing
  (map format, list format, mixed types, edge cases)

First test files for config_cmd.go and http_server.go utilities.

cmd/pulse-sensor-proxy/config_cmd_test.go

@@ -0,0 +1,160 @@
+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestExtractNodesFromYAML(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected []string
+	}{
+		// Map format with allowed_nodes key
+		{
+			name: "map format with allowed_nodes key",
+			input: `allowed_nodes:
+  - node1
+  - node2
+  - node3`,
+			expected: []string{"node1", "node2", "node3"},
+		},
+		{
+			name: "map format with other keys",
+			input: `metrics_address: 127.0.0.1:9127
+allowed_nodes:
+  - host1
+  - host2
+ssh_timeout: 30s`,
+			expected: []string{"host1", "host2"},
+		},
+		{
+			name: "map format empty allowed_nodes",
+			input: `allowed_nodes: []
+other_key: value`,
+			expected: nil,
+		},
+
+		// List format (bare YAML list)
+		{
+			name: "list format bare",
+			input: `- node1
+- node2
+- node3`,
+			expected: []string{"node1", "node2", "node3"},
+		},
+		{
+			name: "list format single item",
+			input: `- single-node`,
+			expected: []string{"single-node"},
+		},
+
+		// Empty and edge cases
+		{
+			name:     "empty input",
+			input:    ``,
+			expected: nil,
+		},
+		{
+			name:     "only whitespace",
+			input:    `   `,
+			expected: nil,
+		},
+		{
+			name: "empty strings filtered",
+			input: `allowed_nodes:
+  - node1
+  - ""
+  - node2`,
+			expected: []string{"node1", "node2"},
+		},
+		{
+			name: "null value in list",
+			input: `allowed_nodes:
+  - node1
+  - ~
+  - node2`,
+			expected: []string{"node1", "node2"},
+		},
+		{
+			name:     "invalid YAML",
+			input:    `{{{invalid`,
+			expected: nil,
+		},
+
+		// Mixed content
+		{
+			name: "map format with comments",
+			input: `# This is a comment
+allowed_nodes:
+  - node1
+  # inline comment
+  - node2`,
+			expected: []string{"node1", "node2"},
+		},
+		{
+			name: "map format allowed_nodes not a list",
+			input: `allowed_nodes: not-a-list`,
+			expected: nil,
+		},
+
+		// Different YAML structures
+		{
+			name: "nested structure ignored",
+			input: `config:
+  allowed_nodes:
+    - nested-node`,
+			expected: nil, // only top-level allowed_nodes is recognized
+		},
+		{
+			name:     "just null",
+			input:    `~`,
+			expected: nil,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			result := extractNodesFromYAML([]byte(tc.input))
+
+			if !reflect.DeepEqual(result, tc.expected) {
+				t.Errorf("extractNodesFromYAML() = %v, want %v", result, tc.expected)
+			}
+		})
+	}
+}
+
+func TestExtractNodesFromYAML_WithNumericValues(t *testing.T) {
+	// YAML can have non-string values in lists
+	input := `allowed_nodes:
+  - node1
+  - 12345
+  - true
+  - node2`
+
+	result := extractNodesFromYAML([]byte(input))
+
+	// Only string values should be extracted
+	expected := []string{"node1", "node2"}
+	if !reflect.DeepEqual(result, expected) {
+		t.Errorf("extractNodesFromYAML() = %v, want %v", result, expected)
+	}
+}
+
+func TestExtractNodesFromYAML_ListWithMixedTypes(t *testing.T) {
+	// Bare list with mixed types
+	input := `- host1
+- 42
+- host2
+- null
+- host3`
+
+	result := extractNodesFromYAML([]byte(input))
+
+	// Only non-empty strings should be extracted
+	expected := []string{"host1", "host2", "host3"}
+	if !reflect.DeepEqual(result, expected) {
+		t.Errorf("extractNodesFromYAML() = %v, want %v", result, expected)
+	}
+}