Abort a test on nil containers, so that future tests don't panic

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

Closes: #1111
Approved by: baude

vendor/github.com/stretchr/testify/require/forward_requirements.go

@@ -0,0 +1,16 @@
+package require
+
+// Assertions provides assertion methods around the
+// TestingT interface.
+type Assertions struct {
+	t TestingT
+}
+
+// New makes a new Assertions object for the specified TestingT.
+func New(t TestingT) *Assertions {
+	return &Assertions{
+		t: t,
+	}
+}
+
+//go:generate go run ../_codegen/main.go -output-package=require -template=require_forward.go.tmpl