RelSubSet's best is not existed in the set

To repro this, add below code in VolcanoPlanner.isValid() which verifies RelSubset.best indeed belongs to its set -

        // Make sure best RelNode is valid
        if (subset.best != null && !subset.set.rels.contains(subset.best)) {
          return litmus.fail("RelSubSet [{}] has best RelNode [{}] which is not existed in its set.",
                  subset.getDescription(), subset.best.getDescription());
        }

Run JDBCTest.testVarcharEquals, you will get below exception -

java.lang.AssertionError: RelSubSet rel#6828:Subset#2.JDBC.foodmart.[] has best RelNode rel#6871:JdbcProject.JDBC.foodmart.[](input=RelSubset#6844,lname=$2) which is not existed in its set.

at org.apache.calcite.util.Litmus$1.fail(Litmus.java:31)
at org.apache.calcite.plan.volcano.VolcanoPlanner.isValid(VolcanoPlanner.java:888)
at org.apache.calcite.plan.volcano.VolcanoPlanner.register(VolcanoPlanner.java:851)
at org.apache.calcite.plan.volcano.VolcanoPlanner.ensureRegistered(VolcanoPlanner.java:868)
at org.apache.calcite.plan.volcano.VolcanoPlanner.ensureRegistered(VolcanoPlanner.java:1939)
at org.apache.calcite.plan.volcano.VolcanoRuleCall.transformTo(VolcanoRuleCall.java:129)
at org.apache.calcite.plan.RelOptRuleCall.transformTo(RelOptRuleCall.java:236)
at org.apache.calcite.rel.convert.ConverterRule.onMatch(ConverterRule.java:141)
at org.apache.calcite.plan.volcano.VolcanoRuleCall.onMatch(VolcanoRuleCall.java:208)
at org.apache.calcite.plan.volcano.VolcanoPlanner.findBestExp(VolcanoPlanner.java:631)
at org.apache.calcite.tools.Programs.lambda$standard$3(Programs.java:286)
at org.apache.calcite.tools.Programs$SequenceProgram.run(Programs.java:346)
at org.apache.calcite.prepare.Prepare.optimize(Prepare.java:189)
at org.apache.calcite.prepare.Prepare.prepareSql(Prepare.java:320)
at org.apache.calcite.prepare.Prepare.prepareSql(Prepare.java:231)
at org.apache.calcite.prepare.CalcitePrepareImpl.prepare2_(CalcitePrepareImpl.java:638)
at org.apache.calcite.prepare.CalcitePrepareImpl.prepare_(CalcitePrepareImpl.java:502)
at org.apache.calcite.prepare.CalcitePrepareImpl.prepareSql(CalcitePrepareImpl.java:472)
at org.apache.calcite.jdbc.CalciteConnectionImpl.parseQuery(CalciteConnectionImpl.java:231)
at org.apache.calcite.jdbc.CalciteMetaImpl.prepareAndExecute(CalciteMetaImpl.java:550)
at org.apache.calcite.avatica.AvaticaConnection.prepareAndExecuteInternal(AvaticaConnection.java:675)
at org.apache.calcite.avatica.AvaticaStatement.executeInternal(AvaticaStatement.java:156)
at org.apache.calcite.avatica.AvaticaStatement.executeQuery(AvaticaStatement.java:227)
at org.apache.calcite.test.CalciteAssert.assertQuery(CalciteAssert.java:522)
at org.apache.calcite.test.CalciteAssert$AssertQuery.lambda$returns$1(CalciteAssert.java:1466)
at org.apache.calcite.test.CalciteAssert$AssertQuery.withConnection(CalciteAssert.java:1398)
at org.apache.calcite.test.CalciteAssert$AssertQuery.returns(CalciteAssert.java:1464)
at org.apache.calcite.test.CalciteAssert$AssertQuery.returns(CalciteAssert.java:1447)
at org.apache.calcite.test.CalciteAssert$AssertQuery.returns(CalciteAssert.java:1410)
at org.apache.calcite.test.JdbcTest.testVarcharEquals(JdbcTest.java:4420)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Suppressed: org.apache.calcite.util.TestUtil$ExtraInformation: With materializationsEnabled=false, limit=0, sql=select count as c from "customer" where "lname" = 'this string is longer than 30 characters'
at org.apache.calcite.util.TestUtil.rethrow(TestUtil.java:268)
at org.apache.calcite.test.CalciteAssert.assertQuery(CalciteAssert.java:554)
... 28 more