diff --git a/Makefile b/Makefile
index 5eb55a9eb..317e4ef22 100644
--- a/Makefile
+++ b/Makefile
@@ -111,10 +111,11 @@ build_for_integration_test:
 	) || (make failpoint-disable && exit 1)
 	@make failpoint-disable
 
+test: export ARGS=$$($(PACKAGES))
 test:
 	$(PREPARE_MOD)
 	@make failpoint-enable
-	$(GOTEST) $(RACEFLAG) -tags leak $$($(PACKAGES)) || ( make failpoint-disable && exit 1 )
+	$(GOTEST) $(RACEFLAG) -tags br_test,leak $(ARGS) || ( make failpoint-disable && exit 1 )
 	@make failpoint-disable
 
 testcover: tools
@@ -188,7 +189,7 @@ static: prepare tools
 	@#   exhaustivestruct - Protobuf structs have hidden fields, like "XXX_NoUnkeyedLiteral"
 	@#         exhaustive - no need to check exhaustiveness of enum switch statements
 	@#              gosec - too many false positive
-	CGO_ENABLED=0 tools/bin/golangci-lint run --enable-all --deadline 120s \
+	CGO_ENABLED=0 tools/bin/golangci-lint run --enable-all --build-tags br_test --deadline 120s \
 		--disable gochecknoglobals \
 		--disable goimports \
 		--disable gofmt \
diff --git a/pkg/mock/backend.go b/pkg/mock/backend.go
index 8f69935c3..4b30c66f9 100644
--- a/pkg/mock/backend.go
+++ b/pkg/mock/backend.go
@@ -1,6 +1,8 @@
 // Code generated by MockGen. DO NOT EDIT.
 // Source: github.com/pingcap/br/pkg/lightning/backend (interfaces: AbstractBackend,Encoder,Rows,Row,EngineWriter)
 
+//+build br_test
+
 // $ mockgen -package mock -mock_names 'AbstractBackend=MockBackend' github.com/pingcap/br/pkg/lightning/backend AbstractBackend,Encoder,Rows,Row,EngineWriter
 
 // Package mock is a generated GoMock package.
diff --git a/pkg/mock/dummy.go b/pkg/mock/dummy.go
new file mode 100644
index 000000000..21b43d21e
--- /dev/null
+++ b/pkg/mock/dummy.go
@@ -0,0 +1,5 @@
+// Copyright 2021 PingCAP, Inc. Licensed under Apache-2.0.
+
+// This file avoids mock being an empty package when `-tags br_test` is not provided.
+
+package mock
diff --git a/pkg/mock/glue.go b/pkg/mock/glue.go
index 63ece855e..2c5f74bf5 100644
--- a/pkg/mock/glue.go
+++ b/pkg/mock/glue.go
@@ -1,6 +1,8 @@
 // Code generated by MockGen. DO NOT EDIT.
 // Source: github.com/pingcap/br/pkg/lightning/glue/glue.go
 
+//+build br_test
+
 // Package mock is a generated GoMock package.
 package mock
 
@@ -8,12 +10,12 @@ import (
 	context "context"
 	sql "database/sql"
 	gomock "github.com/golang/mock/gomock"
-	parser "github.com/pingcap/parser"
-	model "github.com/pingcap/parser/model"
 	checkpoints "github.com/pingcap/br/pkg/lightning/checkpoints"
 	config "github.com/pingcap/br/pkg/lightning/config"
 	glue "github.com/pingcap/br/pkg/lightning/glue"
 	log "github.com/pingcap/br/pkg/lightning/log"
+	parser "github.com/pingcap/parser"
+	model "github.com/pingcap/parser/model"
 	reflect "reflect"
 )
 
diff --git a/pkg/mock/glue_checkpoint.go b/pkg/mock/glue_checkpoint.go
index 50bf3fc36..73df5c4e8 100644
--- a/pkg/mock/glue_checkpoint.go
+++ b/pkg/mock/glue_checkpoint.go
@@ -1,6 +1,8 @@
 // Code generated by MockGen. DO NOT EDIT.
 // Source: github.com/pingcap/br/pkg/lightning/checkpoints/glue_checkpoint.go
 
+//+build br_test
+
 // Package mock is a generated GoMock package.
 package mock
 
diff --git a/pkg/mock/importer.go b/pkg/mock/importer.go
index a58c0d05b..50c9611f8 100644
--- a/pkg/mock/importer.go
+++ b/pkg/mock/importer.go
@@ -1,6 +1,8 @@
 // Code generated by MockGen. DO NOT EDIT.
 // Source: github.com/pingcap/kvproto/pkg/import_kvpb (interfaces: ImportKVClient,ImportKV_WriteEngineClient)
 
+//+build br_test
+
 // $ mockgen -package mock github.com/pingcap/kvproto/pkg/import_kvpb ImportKVClient,ImportKV_WriteEngineClient
 
 // Package mock is a generated GoMock package.
diff --git a/pkg/mock/mock_cluster.go b/pkg/mock/mock_cluster.go
index 46e4048fd..c5c4c0992 100644
--- a/pkg/mock/mock_cluster.go
+++ b/pkg/mock/mock_cluster.go
@@ -1,5 +1,7 @@
 // Copyright 2020 PingCAP, Inc. Licensed under Apache-2.0.
 
+//+build br_test
+
 package mock
 
 import (
diff --git a/pkg/mock/mock_cluster_test.go b/pkg/mock/mock_cluster_test.go
index 2ca00923c..9e5455383 100644
--- a/pkg/mock/mock_cluster_test.go
+++ b/pkg/mock/mock_cluster_test.go
@@ -1,5 +1,7 @@
 // Copyright 2020 PingCAP, Inc. Licensed under Apache-2.0.
 
+//+build br_test
+
 package mock_test
 
 import (
diff --git a/pkg/mock/s3iface.go b/pkg/mock/s3iface.go
index e8151f124..3b65420a0 100644
--- a/pkg/mock/s3iface.go
+++ b/pkg/mock/s3iface.go
@@ -1,6 +1,8 @@
 // Code generated by MockGen. DO NOT EDIT.
 // Source: github.com/aws/aws-sdk-go/service/s3/s3iface (interfaces: S3API)
 
+//+build br_test
+
 // $ mockgen -package mock github.com/aws/aws-sdk-go/service/s3/s3iface S3API > pkg/mock/s3iface.go
 
 // Package mock is a generated GoMock package.
diff --git a/pkg/mock/storage.go b/pkg/mock/storage.go
index a41f6ac37..2aede68a8 100644
--- a/pkg/mock/storage.go
+++ b/pkg/mock/storage.go
@@ -1,7 +1,11 @@
 // Code generated by MockGen. DO NOT EDIT.
 // Source: github.com/pingcap/br/pkg/storage (interfaces: ExternalStorage)
 
+<<<<<<< HEAD:pkg/lightning/mock/storage.go
 // $ mockgen -package mock github.com/pingcap/br/pkg/storage ExternalStorage
+=======
+//+build br_test
+>>>>>>> 969b420... mock: enable the mock package only in unit tests (#838):pkg/mock/storage.go
 
 // Package mock is a generated GoMock package.
 package mock
diff --git a/tests/README.md b/tests/README.md
index b6d238aa1..5030a8f7b 100644
--- a/tests/README.md
+++ b/tests/README.md
@@ -1,8 +1,38 @@
-This folder contains all tests which relies on external processes such as TiDB.
+# Unit tests
 
 Unit tests (the `*_test.go` files inside the source directory) should *never* rely on external
 programs.
 
+Run `make test` to execute all unit tests.
+
+To run a specific test, pass `ARGS` into `make test` like
+
+```sh
+make test ARGS='github.com/pingcap/br/pkg/cdclog --test.v --check.v --check.f TestColumn'
+#               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+#                which package to test            more extra test flags
+```
+
+You can also run unit tests directly via `go test` like:
+
+```sh
+make failpoint-enable
+
+go test -tags br_test github.com/pingcap/br/pkg/cdclog --test.v --check.v --check.f TestColumn
+#       ^~~~~~~~~~~~~
+
+make failpoint-disable
+```
+
+but note that:
+
+* the build-tag `br_test` must be enabled (this workarounds the lack of test-dependencies in go.mod)
+* failpoints must be toggled manually
+
+# Integration tests
+
+This folder contains all tests which relies on external processes such as TiDB.
+
 ## Preparations
 
 1. The following 9 executables must be copied or linked into these locations:
@@ -39,7 +69,6 @@ If you have docker installed, you can skip step 1 and step 2 by running
 
 ## Running
 
-Run `make test` to execute the unit tests.
 Run `make integration_test` to execute the integration tests. This command will
 
 1. Build `br`