Add versioning to perf SQL database

perf/go/db/db_test.go

+package db
+
+import (
+        "fmt"
+        "os"
+        "testing"
+)
+
+import (
+        // Using 'require' which is like using 'assert' but causes tests to fail.
+        assert "github.com/stretchr/testify/require"
+)
+
+// Connection string to the local MySQL database for testing.

[jcgregorio, 2014/09/30 14:54:08]

So I need a local MySQL instance to run this test?

[stephana, 2014/09/30 18:11:50]

Yes. I have changed it so that it checks whether the env variable is set and
skips the test with a log message if not set. 
(and still test against SQLite).

+const MYSQL_DB_OPEN = "root:%s@tcp(localhost:3306)/skia?parseTime=true"
+
+func TestDBVersioning(t *testing.T) {
+        // Initialize without argument to test against SQLite3
+        Init("")
+        assert.False(t, isMySQL)
+        testDBVersioning(t)
+
+        // Initialize to test against local MySQL db
+        Init(fmt.Sprintf(MYSQL_DB_OPEN, os.Getenv("MYSQL_TESTING_ROOTPW")))
+        assert.True(t, isMySQL)
+        testDBVersioning(t)
+}
+
+// Test wether the migration scripts execute.
+func testDBVersioning(t *testing.T) {
+        // get the DB version
+        dbVersion, err := DBVersion()
+        assert.Nil(t, err)
+        maxVersion := MaxDBVersion()
+
+        // downgrade to 0
+        err = Migrate(0)
+        assert.Nil(t, err)
+        dbVersion, err = DBVersion()
+        assert.Nil(t, err)
+        assert.Equal(t, 0, dbVersion)
+
+        // upgrade the the latest version
+        err = Migrate(maxVersion)
+        assert.Nil(t, err)
+        dbVersion, err = DBVersion()
+        assert.Nil(t, err)
+        assert.Equal(t, maxVersion, dbVersion)
+}