tests: Refactor test that no backtraces are collected for skipped specs

The "should not generate backtraces for skipped specs" had a lot of
similarties to the two specs in the "should not be collected or
printed for" suite.  Move it into that suite, not only for shared code
but also because they balong together.

tests/test-buttercup.el

@@ -2006,6 +2006,24 @@ before it's processed by other functions."
       (expect 'buttercup--backtrace :not :to-have-been-called)
       ;; Checking both if buttercup--backtrace have been called and
       ;; the failure-stack value might be overkill
+      (expect (cl-every #'null
+                        (mapcar #'buttercup-spec-failure-stack
+                                (buttercup-suite-children (car test-suites)))))
+      (expect (buttercup-output) :to-equal ""))
+    (it "skipped specs"
+      (with-local-buttercup
+       :reporter #'backtrace-reporter
+        (describe "one description with"
+          (it "one skipped spec"
+            (buttercup-skip "skip"))
+          (xit "one empty spec")
+          (it "one un-assumed spec"
+            (assume nil "A very unassuming spec")))
+        (buttercup-run :noerror)
+        (setq test-suites buttercup-suites))
+      (expect 'buttercup--backtrace :not :to-have-been-called)
+      ;; Checking both if buttercup--backtrace have been called and
+      ;; the failure-stack value might be overkill
       (expect (cl-every #'null
                         (mapcar #'buttercup-spec-failure-stack
                                 (buttercup-suite-children (car test-suites)))))
@@ -2159,18 +2177,7 @@ before it's processed by other functions."
       (matcher-spec ":to-have-been-called-with" :to-have-been-called-with 2)
       (matcher-spec ":not :to-have-been-called-with" :not :to-have-been-called-with 2)
       (matcher-spec ":to-have-been-called-times" :to-have-been-called-times 2)
-      (matcher-spec ":not :to-have-been-called-times" :not :to-have-been-called-times 2)))
-  (it "should not generate backtraces for skipped specs"
-    (let (test-spec)
-      (spy-on 'buttercup--backtrace :and-call-through)
-      (with-local-buttercup
-        (describe "one description"
-          (it "with a pending spec")
-          (buttercup-skip "skip"))
-        (buttercup-run :noerror)
-        (setq test-spec (car (buttercup-suite-children (car buttercup-suites)))))
-      (expect 'buttercup--backtrace :not :to-have-been-called)
-      (expect (buttercup-spec-failure-stack test-spec) :to-be nil))))
+      (matcher-spec ":not :to-have-been-called-times" :not :to-have-been-called-times 2))))
 
 
 (describe "When using quiet specs in the batch reporter"