Although fallbacks to the cpu backend have been implemented, trying to
test RooFit without clad leads to a gtest failure, since the test suite
will be instantiated three times with the same backend.

This makes TEfficiency consistent with other histogram-like classes, in
the sense that it only adds itself to a directory if the corresponding
flags are on.

Diffs of the outputs are fragile, so the ownership of histograms is now
tested programmatically.

If implicit object ownership gets in TDirectories gets switched off, the
example histograms need to be added to directories or written
explicitly.

- Explain that implicit assignment to directories is likely off in R7.
- Make the test insensitive to any defaults by always adding the
  histogram to the file.

Slightly adapt ownership test to be independent of whether ROOT's
implicit ownership settings are on or off.

When histograms get added to a THStack, they are likely in multiple
TLists. Therefore, the kMustCleanup bit must be set.
In the past, the bit usually got set automatically when histograms added
themselves to directories, but when this is disabled, the cleanup bit
remained unset.

Also add an assertion to stop the test when executed in the wrong
directory. Previously, the test would crash.

The test broke when implicit object ownership was switched off in ROOT.
However, this test can also break in other circumstances, because
   del histogram
generally does not destroy the C++ object immediately. It used to work
because only a single reference to the object was alive (which changed
when trying to prepare the test for implicit object ownership off), but
one cannot base a test on undocumented details of a Python implementation.

For this reason, it does not make sense to test if gDirectory (C++)
contains an entry for the object that was just "del"-ed.

When calling TDirectory::Append(obj, replace=true), and obj is already
in the directory, return without doing anything.
If obj has the same name as an existing object, but is physically
different, the usual warning is raised.

This will enable workflows such as:
   auto h = new TH1D(...);
   directory->Append(h, true);

After this change, the above lines work both with implicit object
ownership off and on. This pattern will allow writing robust programs
with consistent behaviour.

Explicitly assign histograms to directories. In this way, the tests
proceed irrespective of whether or not implicit object ownership is in
use.

The test was relying on implicit ownership to transfer a histogram from
python to C++, so now the histogram is appended explicitly.

When implicit histogram ownership is off, the co-ownership of a function
both by the global list of functions and by a histogram lead to a double
delete.

The tutorial was running code that didn't directly reference the
histogram, so it failed when implicit ownership is off.

- Add a silentOff mode for running tests that check the program output.

…ived.

- Couple TH1::AddDirectoryStatus to
  ROOT::DisableImplicitObjectOwnership.
- Add a manual exception for TTree::Draw(): Histograms and profiles will
  still register themselves to gDirectory because the registration is an
  essential part of the feature.

- Use non-zero exit code when a test fails.
- When a test fails, print the file name of the generated graphics.
- Label all stressGraphics runs as longtest.
- Print differences in SVGs similar to how a unified diff would be
  printed.

In the past, stressGraphics was retrieving a histogram from a file,
modifying it and drawing it. In subsequent tests, the histogram is again
read from the TFile, but this returns the in-memory object. This means
that the previous tests influence the subsequent tests, e.g. whether or
not statistics objects are displayed.
In particular, subsequent tests will have the statistics box drawn
twice, once from THistPainter::PaintStat(), and once from the fact that
the box is added to the list of functions. This impacts output files
such as PDF/PS/SVG.

Here, the histogram is always cloned when it is retrieved from the file,
so the tests are independent. The reference files for SVG are
regenerated, because the statistics box is now only drawn once.
Similarly, the output size of the .ps files has been corrected to
reflect that the boxes are only drawn once.