Add validation for names like '-'

- Added unit tests for new implementation
- Updated godoc

Signed-off-by: Madhav Jivrajani <madhav.jiv@gmail.com>

staging/src/k8s.io/apimachinery/pkg/api/validation/generic.go

@@ -68,9 +68,11 @@ var ValidateNamespaceName = NameIsDNSLabel
 var ValidateServiceAccountName = NameIsDNSSubdomain
 
 // maskTrailingDash replaces the final character of a string with a subdomain safe
-// value if is a dash.
+// value if it is a dash and if the length of this string is greater than 1. Note that
+// this is used when a value could be appended to the string, see ValidateNameFunc
+// for more info.
 func maskTrailingDash(name string) string {
-	if strings.HasSuffix(name, "-") {
+	if len(name) > 1 && strings.HasSuffix(name, "-") {
 		return name[:len(name)-2] + "a"
 	}
 	return name

staging/src/k8s.io/apimachinery/pkg/api/validation/generic_test.go

@@ -0,0 +1,65 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package validation
+
+import "testing"
+
+func TestMaskTrailingDash(t *testing.T) {
+	testCases := []struct {
+		beforeMasking        string
+		expectedAfterMasking string
+		description          string
+	}{
+		{
+			beforeMasking:        "",
+			expectedAfterMasking: "",
+			description:          "empty string",
+		},
+		{
+			beforeMasking:        "-",
+			expectedAfterMasking: "-",
+			description:          "only a single dash",
+		},
+		{
+			beforeMasking:        "-foo",
+			expectedAfterMasking: "-foo",
+			description:          "has leading dash",
+		},
+		{
+			beforeMasking:        "-foo-",
+			expectedAfterMasking: "-foa",
+			description:          "has both leading and trailing dashes",
+		},
+		{
+			beforeMasking:        "b-",
+			expectedAfterMasking: "a",
+			description:          "has trailing dash",
+		},
+		{
+			beforeMasking:        "ab",
+			expectedAfterMasking: "ab",
+			description:          "has neither leading nor trailing dashes",
+		},
+	}
+
+	for _, tc := range testCases {
+		afterMasking := maskTrailingDash(tc.beforeMasking)
+		if afterMasking != tc.expectedAfterMasking {
+			t.Errorf("error in test case: %s. expected: %s, actual: %s", tc.description, tc.expectedAfterMasking, afterMasking)
+		}
+	}
+}