util/stmtsummary: migrate test-infra to testify

[feitian124]

What problem does this PR solve?

Issue Number: close #26420

Release note

None

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[feitian124]

/cc @tisonkun
hi, please help review, thanks

[tisonkun]

@feitian124 thanks for your contribution @feitian124 ! I'll review this PR tomorrow.

[feitian124]

@tisonkun ok, thanks

[tisonkun]

Can you separate statement_summary_test.go changes into another PR? This PR is too large to review.

[feitian124]

sorry, it is large and take me some time to finish...
but i am not sure how to separate them to 2 pr as they solve 1 issue， and if put them in 2 different branch the unit test will fail without aditional work.

i did reorder my commit and pushed to a new branch https://github.com/feitian124/tidb/commits/issue-26420-new,
so statement_summary_test.go is in an separate commit.

commit f01914e8ecf743b3a22edf81a49ed25eb9ac6c7d (HEAD -> issue-26420-new, my/issue-26420-new, issue-26420-part1)
Author: feitian124 <feitian124@gmail.com>
Date:   Tue Aug 3 13:32:11 2021 +0800

    util/stmtsummary: migrate test-infra to testify, part 2

 util/stmtsummary/evicted_test.go   | 143 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-------------------------------------------------------------------
 util/stmtsummary/main_test.go      |  26 ++++++++++++++++++++++++++
 util/stmtsummary/variables_test.go |  98 +++++++++++++++++++++++++++++++++++++++++++++++++-------------------------------------------------
 3 files changed, 151 insertions(+), 116 deletions(-)

commit 68a3829fefe77aa229af61963710366bfe452120
Author: feitian124 <feitian124@gmail.com>
Date:   Tue Aug 3 13:32:00 2021 +0800

    util/stmtsummary: migrate test-infra to testify, part 1

 util/stmtsummary/statement_summary_test.go | 615 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-------------------------------------------------------------------------------------------
 1 file changed, 311 insertions(+), 304 deletions(-)

not sure if this help.
if this is what you want, i can create a new pr based on issue-26420-new and close this pr.
if this is not what you want, please give some guide.
thanks.

[tisonkun]

@feitian124 you can take a look at how we do it for domain pkg #26306, or if you separate in multiple commits in one PR said this one, it is fine also.

[tisonkun]

Here is an example how to break diff into meaningful commits that helps on reviewing. https://github.com/apache/flink/pull/9832/commits

[feitian124]

@feitian124 you can take a look at how we do it for domain pkg #26306, or if you separate in multiple commits in one PR said this one, it is fine also.

hi @tisonkun , i have separate them to 3 pr, hopefully can make your review easier.