Replace gopkg.in/check.v1 by github.com/stretchr/testify/suite/

gopkg.in/check.v1 hasn't had any commit since Nov 2020.
That's not a immediate issue for a test-only dependency, but
because it hides access to the standard library *testing.T,
eventually it will become limiting.

Also, using the same framework for unit and integration tests
seems practical.

This is mostly a batch copy&paste job, with a fairly high risk
of unexpected breakage.

Also, I didn't take much time at all to carefully choose between
assert.* and require.*; we can tune that as failures show up.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

vendor/github.com/stretchr/testify/suite/interfaces.go

@@ -0,0 +1,53 @@
+package suite
+
+import "testing"
+
+// TestingSuite can store and return the current *testing.T context
+// generated by 'go test'.
+type TestingSuite interface {
+	T() *testing.T
+	SetT(*testing.T)
+}
+
+// SetupAllSuite has a SetupSuite method, which will run before the
+// tests in the suite are run.
+type SetupAllSuite interface {
+	SetupSuite()
+}
+
+// SetupTestSuite has a SetupTest method, which will run before each
+// test in the suite.
+type SetupTestSuite interface {
+	SetupTest()
+}
+
+// TearDownAllSuite has a TearDownSuite method, which will run after
+// all the tests in the suite have been run.
+type TearDownAllSuite interface {
+	TearDownSuite()
+}
+
+// TearDownTestSuite has a TearDownTest method, which will run after
+// each test in the suite.
+type TearDownTestSuite interface {
+	TearDownTest()
+}
+
+// BeforeTest has a function to be executed right before the test
+// starts and receives the suite and test names as input
+type BeforeTest interface {
+	BeforeTest(suiteName, testName string)
+}
+
+// AfterTest has a function to be executed right after the test
+// finishes and receives the suite and test names as input
+type AfterTest interface {
+	AfterTest(suiteName, testName string)
+}
+
+// WithStats implements HandleStats, a function that will be executed
+// when a test suite is finished. The stats contain information about
+// the execution of that suite and its tests.
+type WithStats interface {
+	HandleStats(suiteName string, stats *SuiteInformation)
+}