chore: register a default mock result for column defaults

The Spanner Liquibase provider executes an extra query to get the column
default value, as the Spanner JDBC driver does not include that in the
metadata it returns.

This will be fixed in googleapis/java-spanner-jdbc#1937

Author: olavloite

src/main/java/liquibase/ext/spanner/snapshotgenerator/ColumnSnapshotGeneratorSpanner.java

@@ -40,6 +40,7 @@ protected Object readDefaultValue(
       CachedRow columnMetadataResultSet, Column columnInfo, Database database) {
     if (database instanceof ICloudSpanner) {
       try {
+        // TODO: Remove when COLUMN_DEF is included in the results for getColumns
         String selectQuery =
             "SELECT DISTINCT COLUMN_DEFAULT AS COLUMN_DEF FROM INFORMATION_SCHEMA.COLUMNS "
                 + "WHERE TABLE_CATALOG = ? "

src/test/java/liquibase/ext/spanner/AbstractMockServerTest.java

@@ -14,6 +14,7 @@
 import com.google.protobuf.Any;
 import com.google.protobuf.Empty;
 import com.google.protobuf.ListValue;
+import com.google.protobuf.NullValue;
 import com.google.protobuf.Value;
 import com.google.spanner.admin.database.v1.UpdateDatabaseDdlMetadata;
 import com.google.spanner.admin.database.v1.UpdateDatabaseDdlRequest;
@@ -76,6 +77,10 @@ public abstract class AbstractMockServerTest {
       Statement.of(
           "INSERT INTO DATABASECHANGELOG (ID, AUTHOR, FILENAME, DATEEXECUTED, ORDEREXECUTED, MD5SUM, DESCRIPTION, COMMENTS, EXECTYPE, CONTEXTS, LABELS, LIQUIBASE, DEPLOYMENT_ID)");
 
+  static final Statement GET_COLUMN_DEFAULT_STATEMENT =
+      Statement.of(
+          "SELECT DISTINCT COLUMN_DEFAULT AS COLUMN_DEF FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_CATALOG = @p1 AND TABLE_SCHEMA = @p2 AND TABLE_NAME = @p3 AND COLUMN_NAME = @p4");
+
   private static final ResultSetMetadata SINGLE_COL_INT64_METADATA =
       ResultSetMetadata.newBuilder()
           .setRowType(
@@ -324,6 +329,28 @@ private static void registerDefaultResults() {
     mockSpanner.putStatementResult(
         StatementResult.query(SELECT_MAX_ORDER_EXEC, createInt64ResultSet(0L)));
     mockSpanner.putPartialStatementResult(StatementResult.update(INSERT_DATABASECHANGELOG, 1L));
+
+    // TODO: Remove when the JDBC driver includes the column default in getColumns
+    mockSpanner.putPartialStatementResult(
+        StatementResult.query(
+            GET_COLUMN_DEFAULT_STATEMENT,
+            ResultSet.newBuilder()
+                .setMetadata(
+                    ResultSetMetadata.newBuilder()
+                        .setRowType(
+                            StructType.newBuilder()
+                                .addFields(
+                                    Field.newBuilder()
+                                        .setName("COLUMN_DEF")
+                                        .setType(Type.newBuilder().setCode(TypeCode.STRING).build())
+                                        .build())
+                                .build())
+                        .build())
+                .addRows(
+                    ListValue.newBuilder()
+                        .addValues(Value.newBuilder().setNullValue(NullValue.NULL_VALUE).build())
+                        .build())
+                .build()));
   }
 
   @AfterAll