test: 补充单元测试覆盖率 29.9% → 36.6%

新建 18 个测试文件，追加 30 个已有测试文件，覆盖协议解析、
错误分类、CEL 表达式求值、YAML 反序列化、字节编码等纯函数。

plugins/services/cassandra_test.go

@@ -5,6 +5,7 @@ package services
 import (
 	"bytes"
 	"encoding/binary"
+	"errors"
 	"strings"
 	"testing"
 )
@@ -47,3 +48,74 @@ func TestValidateCQLQueryResponseRejectsErrors(t *testing.T) {
 		t.Fatal("validateCQLQueryResponse() error = nil, want unexpected opcode error")
 	}
 }
+
+func TestClassifyCassandraErrorType(t *testing.T) {
+	tests := []struct {
+		name string
+		err  error
+		want ErrorType
+	}{
+		{"nil", nil, ErrorTypeUnknown},
+		{"auth error", errors.New("authentication failed"), ErrorTypeAuth},
+		{"bad credentials", errors.New("bad credentials"), ErrorTypeAuth},
+		{"network error", errors.New("connection refused"), ErrorTypeNetwork},
+		{"unknown", errors.New("random cassandra error"), ErrorTypeUnknown},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := classifyCassandraErrorType(tt.err); got != tt.want {
+				t.Errorf("classifyCassandraErrorType() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestCqlShortString(t *testing.T) {
+	got := cqlShortString("AB")
+	if len(got) != 4 || binary.BigEndian.Uint16(got[:2]) != 2 || string(got[2:]) != "AB" {
+		t.Errorf("cqlShortString(AB) = %v", got)
+	}
+	empty := cqlShortString("")
+	if len(empty) != 2 || binary.BigEndian.Uint16(empty) != 0 {
+		t.Errorf("cqlShortString empty = %v", empty)
+	}
+}
+
+func TestCqlLongString(t *testing.T) {
+	got := cqlLongString("XYZ")
+	if len(got) != 7 || binary.BigEndian.Uint32(got[:4]) != 3 || string(got[4:]) != "XYZ" {
+		t.Errorf("cqlLongString(XYZ) = %v", got)
+	}
+}
+
+func TestCqlStringMap(t *testing.T) {
+	m := map[string]string{"k": "v"}
+	got := cqlStringMap(m)
+	if got[0] != 0x00 || got[1] != 0x01 {
+		t.Errorf("count bytes wrong: %v", got[:2])
+	}
+	if !bytes.Contains(got, []byte("k")) || !bytes.Contains(got, []byte("v")) {
+		t.Errorf("missing key/value in %v", got)
+	}
+}
+
+func TestExtractClusterName(t *testing.T) {
+	tests := []struct {
+		name string
+		data []byte
+		want string
+	}{
+		{"empty", nil, "unknown"},
+		{"short", []byte{0x01, 0x02}, "unknown"},
+		{"printable", append([]byte{0x00, 0x00, 0x00, 0x01}, []byte("TestCluster")...), "TestCluster"},
+		{"binary prefix", append([]byte{0x00, 0x00, 0x00, 0x00, 0x01, 0x02}, []byte("MyCluster")...), "MyCluster"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := extractClusterName(tt.data)
+			if !strings.Contains(got, tt.want) && got != tt.want {
+				t.Errorf("extractClusterName() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}