added foreign keys test

t/39_foreign_keys.t

@@ -0,0 +1,75 @@
+#!/usr/bin/perl
+
+use strict;
+BEGIN {
+	$|  = 1;
+	$^W = 1;
+}
+
+use t::lib::Test;
+use Test::More;
+use Test::NoWarnings;
+
+plan tests => 17;
+
+# following tests are from http://www.sqlite.org/foreignkeys.html
+
+my $dbh = connect_ok( RaiseError => 1, PrintError => 0, AutoCommit => 1 );
+
+$dbh->do("PRAGMA foreign_keys = ON");
+
+ok $dbh->do("CREATE TABLE artist (
+    artistid    INTEGER PRIMARY KEY,
+    artistname  TEXT
+)");
+ok $dbh->do("CREATE TABLE track (
+    trackid     INTEGER PRIMARY KEY,
+    trackname   TEXT,
+    trackartist INTEGER,
+    FOREIGN KEY(trackartist) REFERENCES artist(artistid)
+)");
+
+ok insert_artist(1, "Dean Martin");
+ok insert_artist(2, "Frank Sinatra");
+
+ok insert_track(11, "That's Amore", 1);
+ok insert_track(12, "Christmas Blues", 1);
+ok insert_track(13, "My Way", 2);
+
+# This fails because the value inserted into the trackartist
+# column (3) does not correspond to row in the artist table.
+
+ok !insert_track(14, "Mr. Bojangles", 3);
+ok $@ =~ qr/foreign key constraint failed/;
+
+# This succeeds because a NULL is inserted into trackartist. A
+# corresponding row in the artist table is not required in this case.
+
+ok insert_track(14, "Mr. Bojangles", undef);
+
+# Trying to modify the trackartist field of the record after it has 
+# been inserted does not work either, since the new value of 
+# trackartist (3) still does not correspond to any row in the 
+# artist table.
+
+ok !update_track(3, "Mr. Bojangles");
+ok $@ =~ /foreign key constraint failed/;
+
+# Insert the required row into the artist table. It is then possible
+# to update the inserted row to set trackartist to 3 (since a
+# corresponding row in the artist table now exists).
+
+ok insert_artist(3, "Sammy Davis Jr.");
+ok update_track(3, "Mr. Bojangles");
+
+# Now that "Sammy Davis Jr." (artistid = 3) has been added to the
+# database, it is possible to INSERT new tracks using this artist
+# without violating the foreign key constraint:
+
+ok insert_track(15, "Boogie Woogie", 3);
+
+sub insert_artist { _do("INSERT INTO artist (artistid, artistname) VALUES (?, ?)", @_ ); }
+sub insert_track {  _do("INSERT INTO track (trackid, trackname, trackartist) VALUES (?, ?, ?)", @_); }
+sub update_track {  _do("UPDATE track SET trackartist = ? WHERE trackname = ?", @_); }
+
+sub _do { eval { $dbh->do(shift, undef, @_) }; }