cubicweb #5930028 CubicWebTC.assertDocTestFile is broken [validation pending]

uses self.shell(), which is gone.

priorityimportant
typebug
done in3.21.2
load0.250
load left0.000
closed by#0c492a2720f1 [devtools] fix CubicWebTC.assertDocTestFile (closes #5930028)
patch[devtools] fix CubicWebTC.assertDocTestFile (closes #5930028) [applied]