Update invalid json test value, fix issue in Base64Url validation

Author: buyaa-n

src/libraries/System.Memory/tests/Base64/Base64DecoderUnitTests.cs

@@ -285,7 +285,8 @@ public void BasicDecodingWithNonZeroUnusedBits(string inputString)
             Span<byte> decodedBytes = new byte[Base64.GetMaxDecodedFromUtf8Length(source.Length)];
 
             Assert.False(Base64.IsValid(inputString));
-            Assert.Equal(OperationStatus.InvalidData, Base64.DecodeFromUtf8(source, decodedBytes, out int consumed, out int _));
+            Assert.Equal(OperationStatus.InvalidData, Base64.DecodeFromUtf8(source, decodedBytes, out int _, out int _));
+            Assert.Equal(OperationStatus.InvalidData, Base64.DecodeFromUtf8InPlace(source, out int _));
         }
 
         [Theory]

src/libraries/System.Memory/tests/Base64Url/Base64UrlDecoderUnitTests.cs

@@ -300,11 +300,12 @@ public void BasicDecodingWithFinalBlockTrueKnownInputDone(string inputString, in
         [InlineData("AQIDBAUHCAkKCwwNDxD")]
         public void BasicDecodingWithNonZeroUnusedBits(string inputString)
         {
-            Span<byte> source = Encoding.ASCII.GetBytes(inputString);
+            byte[] source = Encoding.ASCII.GetBytes(inputString);
             Span<byte> decodedBytes = new byte[Base64.GetMaxDecodedFromUtf8Length(source.Length)];
 
-            Assert.False(Base64.IsValid(inputString));
-            Assert.Equal(OperationStatus.InvalidData, Base64.DecodeFromUtf8(source, decodedBytes, out int consumed, out int _));
+            Assert.False(Base64Url.IsValid(inputString));
+            Assert.Equal(OperationStatus.InvalidData, Base64Url.DecodeFromUtf8(source, decodedBytes, out int _, out int _));
+            Assert.Throws<FormatException>(() => Base64Url.DecodeFromUtf8InPlace(source));
         }
 
         [Theory]

src/libraries/System.Private.CoreLib/src/System/Buffers/Text/Base64Helper/Base64ValidatorHelper.cs

@@ -108,19 +108,19 @@ internal static bool IsValid<T, TBase64Validatable>(TBase64Validatable validatab
                         }
                     }
 
-                    int decoded = validatable.DecodeValue(lastChar);
-                    if (paddingCount == 1 && (decoded & 0x03) != 0 ||
-                        paddingCount == 2 && (decoded & 0x0F) != 0)
-                    {
-                        // unused lower bits are not 0, reject input
-                        decodedLength = 0;
-                        return false;
-                    }
-
                     length += paddingCount;
                     break;
                 }
 
+                int decoded = validatable.DecodeValue(lastChar);
+                if (paddingCount == 1 && (decoded & 0x03) != 0 ||
+                    paddingCount == 2 && (decoded & 0x0F) != 0)
+                {
+                    // unused lower bits are not 0, reject input
+                    decodedLength = 0;
+                    return false;
+                }
+
                 if (!validatable.ValidateAndDecodeLength(length, paddingCount, out decodedLength))
                 {
                     goto Fail;

src/libraries/System.Text.Json/tests/System.Text.Json.Tests/JsonBase64TestData.cs

@@ -9,7 +9,7 @@ internal class JsonBase64TestData
     {
         public static IEnumerable<object[]> ValidBase64Tests()
         {
-            yield return new object[] { "\"ABC=\"" };
+            yield return new object[] { "\"ABA=\"" };
             yield return new object[] { "\"AB+D\"" };
             yield return new object[] { "\"ABCD\"" };
             yield return new object[] { "\"ABC/\"" };
@@ -19,9 +19,9 @@ public static IEnumerable<object[]> ValidBase64Tests()
 
         public static IEnumerable<object[]> InvalidBase64Tests()
         {
-            yield return new object[] { "\"ABC===\"" };
-            yield return new object[] { "\"ABC\"" };
-            yield return new object[] { "\"ABC!\"" };
+            yield return new object[] { "\"ABA===\"" };
+            yield return new object[] { "\"ABA\"" };
+            yield return new object[] { "\"ABA!\"" };
             yield return new object[] { GenerateRandomInvalidLargeString(includeEscapedCharacter: true) };
             yield return new object[] { GenerateRandomInvalidLargeString(includeEscapedCharacter: false) };
         }