sessionctx/variable: improve test coverage

sessionctx/variable/mock_globalaccessor_test.go

@@ -45,4 +45,9 @@ func TestMockAPI(t *testing.T) {
 	require.NoError(t, err)
 	err = mock.SetGlobalSysVarOnly(DefaultAuthPlugin, "mysql_native_password")
 	require.NoError(t, err)
+
+	// Test GetTiDBTableValue
+	str, err = mock.GetTiDBTableValue("tikv_gc_life_time")
+	require.NoError(t, err)
+	require.Equal(t, "10m0s", str)
 }

sessionctx/variable/removed_test.go

@@ -0,0 +1,28 @@
+// Copyright 2022 PingCAP, Inc.
+//
+// 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 variable
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestRemovedOpt(t *testing.T) {
+	require.NoError(t, CheckSysVarIsRemoved(TiDBEnable1PC))
+	require.False(t, IsRemovedSysVar(TiDBEnable1PC))
+	require.Error(t, CheckSysVarIsRemoved(tiDBEnableAlterPlacement))
+	require.True(t, IsRemovedSysVar(tiDBEnableAlterPlacement))
+}