Decouple unit test code from business code

[wxiaoguang]

Many unit test code and business code were coupled together.

This PR decouples them.

After this refactoring, we only import testing and assert in unit test code:

$ grep -nr --include "*.go" --exclude "*_test.go" --exclude-dir vendor 'testing"' .
./models/unittest/testdb.go:12:	"testing"
./integrations/html_helper.go:9:	"testing"
./integrations/testlogger.go:14:	"testing"
./modules/test/context_tests.go:14:	"testing"

$ grep -nr --include "*.go" --exclude "*_test.go" --exclude-dir vendor 'assert"' .
./models/unittest/bridge.go:9:	"github.com/stretchr/testify/assert"
./models/unittest/testdb.go:20:	"github.com/stretchr/testify/assert"
./integrations/html_helper.go:12:	"github.com/stretchr/testify/assert"
./modules/test/context_tests.go:23:	"github.com/stretchr/testify/assert"

Some details:

What are Tester and Asserter?

They are intermediate interfaces for this refactoring. There are many assertions in models.CheckConsistencyFor (which calls db.AssertXxx), so we introduce the Tester/Asserter interfaces to decouple CheckConsistencyFor from testing frameworks. Then we do not need to import any testing frameworks for non-unit-test code. The benefit is that we get a clearer and smaller built binary.

Why don't we refactor CheckConsistencyFor directly to get rid of the assertions?

It will be a huge project. There are too many related code of CheckConsistencyFor, which may cause cycle-import problems. The refactoring of CheckConsistencyFor is very difficult to be done in a few PRs. So we now we just make the first step to decouple it from testing framework, and then we can refactor CheckConsistencyFor and related models one by one.

Then, one day, if CheckConsistencyFor is clean enough, we can remove the intermediate interfaces (Tester/Asserter).

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (main@7f80263). Click here to learn what that means.
The diff coverage is 57.56%.

@@           Coverage Diff           @@
##             main   #17623   +/-   ##
=======================================
  Coverage        ?   45.49%           
=======================================
  Files           ?      798           
  Lines           ?    88916           
  Branches        ?        0           
=======================================
  Hits            ?    40452           
  Misses          ?    41965           
  Partials        ?     6499           

Impacted Files	Coverage Δ
models/unittest/testdb.go	11.11% <11.11%> (ø)
models/db/engine.go	33.33% <50.00%> (ø)
models/db/unit_tests.go	68.85% <57.57%> (ø)
modules/unittestbridge/unittestbridge.go	66.66% <66.66%> (ø)
models/unittest/bridge.go	75.00% <75.00%> (ø)
models/unittest/fixtures.go	36.11% <83.33%> (ø)
models/consistency.go	47.69% <98.57%> (ø)

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