Add the experimental dbdata extension.

FossilOrigin-Name: a3ab58832935e1399ecc7e4d8daefa3a6afa6b301792ce7176bc5d7c173510fb

test/dbdata.test

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+# 2019-04-11
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+# This file implements regression tests for SQLite library.  The
+# focus of this file is testing the sqlite_dbpage virtual table.
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix dbdata
+
+ifcapable !vtab||!compound {
+  finish_test
+  return
+}
+db enable_load_extension 1
+if { [catch { db eval { SELECT load_extension('../dbdata') } }] } {
+  finish_test
+  return
+}
+
+do_execsql_test 1.0 {
+  CREATE TABLE T1(a, b);
+  INSERT INTO t1(rowid, a ,b) VALUES(5, 'v', 'five');
+  INSERT INTO t1(rowid, a, b) VALUES(10, 'x', 'ten');
+}
+
+do_execsql_test 1.1 {
+  SELECT pgno, cell, field, quote(value) FROM sqlite_dbdata WHERE pgno=2;
+} {
+  2 0 -1 5 
+  2 0  0 'v' 
+  2 0  1 'five' 
+  2 1 -1 10 
+  2 1  0 'x' 
+  2 1  1 'ten'
+}
+
+set big [string repeat big 2000]
+do_execsql_test 1.2 {
+  INSERT INTO t1 VALUES(NULL, $big);
+  SELECT value FROM sqlite_dbdata WHERE pgno=2 AND cell=2 AND field=1;
+} $big
+
+
+
+finish_test