fix(metadata): update tests and comment to match default fallback in GetMetadataReportByRegistry

GetMetadataReportByRegistry intentionally falls back to the 'default'
report when a specific registryId is not found. This supports standalone
metadata-report configs registered under 'default' being used by named
registries (e.g. nacos, zk). Update tests and doc comment to reflect
this behavior instead of the old 'return nil for unknown id' contract.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: xianingawa-wq

metadata/client_test.go

@@ -99,15 +99,18 @@ func TestGetMetadataFromMetadataReport(t *testing.T) {
 		assert.Equal(t, metadataInfo, got)
 	})
 
-	t.Run("unknown registryId returns error instead of silently using wrong report", func(t *testing.T) {
+	t.Run("unknown registryId falls back to default report", func(t *testing.T) {
 		instances = make(map[string]report.MetadataReport)
 		defaultReport := new(mockMetadataReport)
 		defer defaultReport.AssertExpectations(t)
 		instances["default"] = defaultReport
 
-		// defaultReport must NOT be called — GetMetadataReportByRegistry returns nil for unknown id
-		_, err := GetMetadataFromMetadataReport("1", ins, "nonexistent-registry")
-		require.Error(t, err, "should error when the specific registryId has no registered report")
+		// When the specific registryId is not found, it falls back to "default"
+		// so the default report's GetAppMetadata is called
+		defaultReport.On("GetAppMetadata").Return(metadataInfo, nil).Once()
+		got, err := GetMetadataFromMetadataReport("1", ins, "nonexistent-registry")
+		require.NoError(t, err)
+		assert.Equal(t, metadataInfo, got)
 	})
 
 	t.Run("report error propagated", func(t *testing.T) {

metadata/report_instance.go

@@ -78,11 +78,13 @@ func GetMetadataReport() report.MetadataReport {
 }
 
 // GetMetadataReportByRegistry returns the metadata report bound to the given
-// registry id. When registry is empty the caller has no registry context, so
-// the stable default returned by GetMetadataReport is used. When a specific
-// (non-empty) registry id is given but is not registered, nil is returned so
-// the caller receives an explicit failure rather than silently operating
-// against the wrong registry's report.
+// registry id. When the registry id is empty the caller has no registry context,
+// so the stable default returned by GetMetadataReport is used. When a specific
+// (non-empty) registry id is not found, it falls back to the "default" report
+// if one exists. This handles the common case where a standalone metadata-report
+// config is registered under "default" while named registries (e.g. nacos, zk)
+// need to use it. nil is returned only when neither the specific id nor "default"
+// is registered.
 func GetMetadataReportByRegistry(registry string) report.MetadataReport {
 	if len(registry) == 0 {
 		return GetMetadataReport()

metadata/report_instance_test.go

@@ -211,8 +211,8 @@ func TestGetMetadataReportByRegistry(t *testing.T) {
 	assert.Equal(t, defaultReport, GetMetadataReportByRegistry("default"))
 	// empty string → no registry context → falls through to GetMetadataReport() → "default"
 	assert.Equal(t, defaultReport, GetMetadataReportByRegistry(""))
-	// specific but unknown id → nil (not a silent wrong-registry fallback)
-	assert.Nil(t, GetMetadataReportByRegistry("reg"))
+	// specific but unknown id → falls back to "default"
+	assert.Equal(t, defaultReport, GetMetadataReportByRegistry("reg"))
 }
 
 func TestGetMetadataReportByRegistryFallsBackDeterministically(t *testing.T) {
@@ -226,7 +226,7 @@ func TestGetMetadataReportByRegistryFallsBackDeterministically(t *testing.T) {
 	assert.Equal(t, rA, GetMetadataReportByRegistry("aaa"))
 	assert.Equal(t, rB, GetMetadataReportByRegistry("zzz"))
 
-	// unknown specific id → nil, not the lex-first fallback
+	// unknown specific id → nil when no "default" is registered
 	assert.Nil(t, GetMetadataReportByRegistry("unknown-registry"))
 
 	// empty string → falls through to GetMetadataReport() → lex-first ("aaa" → rA)