address comments

Author: jakeheft

bttest/cmv.go

@@ -3,6 +3,7 @@ package bttest
 import (
 	"encoding/json"
 	"fmt"
+	"log"
 	"os"
 	"regexp"
 	"strconv"
@@ -54,6 +55,11 @@ func LoadCMVConfigs(path string) ([]CMVConfig, error) {
 		if len(c.KeyMapping) == 0 {
 			return nil, fmt.Errorf("CMV config[%d]: key_mapping is required", i)
 		}
+		for j, idx := range c.KeyMapping {
+			if idx < 0 {
+				return nil, fmt.Errorf("CMV config[%d]: key_mapping[%d] is negative (%d)", i, j, idx)
+			}
+		}
 	}
 	return configs, nil
 }
@@ -195,6 +201,8 @@ func (c *cmvInstance) transformKey(sourceKey string) string {
 		if idx < len(parts) {
 			newParts = append(newParts, parts[idx])
 		} else {
+			log.Printf("CMV %q: key_mapping index %d out of bounds for source key %q (%d parts) — check your config",
+				c.config.ViewID, idx, sourceKey, len(parts))
 			newParts = append(newParts, "")
 		}
 	}

bttest/cmv_test.go

@@ -285,6 +285,35 @@ func TestLoadCMVConfigs(t *testing.T) {
 	assert.True(t, configs[0].AppendSourceKey)
 }
 
+func TestLoadCMVConfigsNegativeIndex(t *testing.T) {
+	tmpFile, err := os.CreateTemp("", "cmv-test-*.json")
+	require.NoError(t, err)
+	defer os.Remove(tmpFile.Name())
+
+	content := `[{"source_table":"events","view_id":"events_by_account","key_separator":"#","key_mapping":[-1,0]}]`
+	_, err = tmpFile.WriteString(content)
+	require.NoError(t, err)
+	tmpFile.Close()
+
+	_, err = LoadCMVConfigs(tmpFile.Name())
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "negative")
+}
+
+func TestCMVTransformKeyOutOfBounds(t *testing.T) {
+	inst := &cmvInstance{
+		config: CMVConfig{
+			SourceTable:  "events",
+			ViewID:       "events_by_account",
+			KeySeparator: "#",
+			KeyMapping:   []int{0, 99}, // index 99 is out of bounds
+		},
+	}
+	// Should not panic; out-of-bounds index produces an empty component.
+	got := inst.transformKey("only#two#parts")
+	assert.Equal(t, "only#", got)
+}
+
 func TestParseCMVConfigFromSQL(t *testing.T) {
 	// Standard Bigtable CMV SQL pattern: plain SPLIT (no CAST), _key aliased,
 	// alias appears in ORDER BY to set AppendSourceKey = true.