如何在Sql Server GROUP BY格式化日期按日期排序？

I have a table as follows:

我有一张表如下:

Table: student_test_records

Student    TestDate                    Result
-------    ------------------          -------
A          2015-01-26 17:28:11         Pass
B          2015-01-24 17:28:11         Fail
C          2015-01-26 17:28:11         Pass
D          2015-01-26 17:28:11         Fail
E          2014-05-23 17:28:11         Pass
F          2013-06-23 17:28:11         Pass
G          2014-05-23 17:28:11         Fail
Table: