Address some PR suggestions

Signed-off-by: Tim Vaillancourt <tim@timvaillancourt.com>

go/vt/discovery/healthcheck.go

@@ -100,7 +100,8 @@ var (
 	// How much to sleep between each check.
 	waitAvailableTabletInterval = 100 * time.Millisecond
 
-	errKeyspacesToWatchAndTabletFilters = errors.New("Only one of -keyspaces_to_watch and -tablet_filters may be specified at a time")
+	// errKeyspacesToWatchAndTabletFilters is an error for cases where incompatible filters are defined.
+	errKeyspacesToWatchAndTabletFilters = errors.New("only one of --keyspaces_to_watch and --tablet_filters may be specified at a time")
 )
 
 // See the documentation for NewHealthCheck below for an explanation of these parameters.
@@ -308,7 +309,7 @@ func NewVTGateHealthCheckFilters() (filters TabletFilters, err error) {
 
 		fbs, err := NewFilterByShard(tabletFilters)
 		if err != nil {
-			return nil, fmt.Errorf("Cannot parse tablet_filters parameter: %v", err)
+			return nil, fmt.Errorf("failed to parse tablet_filters value %q: %v", strings.Join(tabletFilters, ","), err)
 		}
 		filters = append(filters, fbs)
 	} else if len(KeyspacesToWatch) > 0 {
@@ -347,7 +348,7 @@ func NewVTGateHealthCheckFilters() (filters TabletFilters, err error) {
 //
 // filters.
 //
-//	Is a one or more filters to apply to healthchecks.
+//	Is one or more filters to apply when determining what tablets we want to stream healthchecks from.
 func NewHealthCheck(ctx context.Context, retryDelay, healthCheckTimeout time.Duration, topoServer *topo.Server, localCell, cellsToWatch string, filters TabletFilter) *HealthCheckImpl {
 	log.Infof("loading tablets for cells: %v", cellsToWatch)
 

go/vt/discovery/healthcheck_test.go

@@ -19,7 +19,6 @@ package discovery
 import (
 	"bytes"
 	"context"
-	"errors"
 	"fmt"
 	"html/template"
 	"io"
@@ -77,7 +76,7 @@ func TestNewVTGateHealthCheckFilters(t *testing.T) {
 		keyspacesToWatch    []string
 		tabletFilters       []string
 		tabletFilterTags    map[string]string
-		expectedError       error
+		expectedError       string
 		expectedFilterTypes []any
 	}{
 		{
@@ -109,12 +108,12 @@ func TestNewVTGateHealthCheckFilters(t *testing.T) {
 			name:             "failKeyspacesToWatchAndFilters",
 			tabletFilters:    []string{"ks1|-80"},
 			keyspacesToWatch: []string{"ks1"},
-			expectedError:    errKeyspacesToWatchAndTabletFilters,
+			expectedError:    errKeyspacesToWatchAndTabletFilters.Error(),
 		},
 		{
 			name:          "failInvalidTabletFilters",
 			tabletFilters: []string{"shouldfail!@!@#"},
-			expectedError: errors.New("Cannot parse tablet_filters parameter: invalid FilterByShard parameter: shouldfail!@!@#"),
+			expectedError: "failed to parse tablet_filters value \"shouldfail!@!@#\": invalid FilterByShard parameter: shouldfail!@!@#",
 		},
 	}
 
@@ -125,7 +124,9 @@ func TestNewVTGateHealthCheckFilters(t *testing.T) {
 			tabletFilterTags = testCase.tabletFilterTags
 
 			filters, err := NewVTGateHealthCheckFilters()
-			assert.Equal(t, testCase.expectedError, err)
+			if testCase.expectedError != "" {
+				assert.EqualError(t, err, testCase.expectedError)
+			}
 			assert.Len(t, filters, len(testCase.expectedFilterTypes))
 			for i, filter := range filters {
 				assert.IsType(t, testCase.expectedFilterTypes[i], filter)

go/vt/events/eventer.go

@@ -0,0 +1,9 @@
+package events
+
+import "vitess.io/vitess/go/vt/proto/vtctldata"
+
+type Eventer interface {
+	ChangeTabletType() error
+	EmergencyReparentShard(req *vtctldata.EmergencyReparentShardRequest, resp *vtctldata.EmergencyReparentShardResponse) error
+	PlannedReparentShard() error
+}