test: Check for some unlikely null dereferences in tests

[ximinez]

High Level Overview of Change

I stumbled upon these couple of places where test code could, but is very unlikely to, dereference a null pointer. I added a simple check to each of them.

Context of Change

This was a random find.

Even though these changes are tiny, I don't think they are insignificant enough to be considered "trivial", so I'm requesting two reviews.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• Tests (you added tests for code that already exists, or your new feature included in this PR)

Before / After

There should be no observable change, as tests aren't currently likely / able to get a null value.

Future Tasks

Maybe there are more of these?

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.1%. Comparing base (23991c9) to head (54dfbb3).

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #5004   +/-   ##
=======================================
  Coverage     76.1%   76.1%           
=======================================
  Files          760     760           
  Lines        61548   61548           
  Branches      8159    8157    -2     
=======================================
+ Hits         46836   46842    +6     
+ Misses       14712   14706    -6     

see 5 files with indirect coverage changes

[ckeshava]

Before line 44 (above), for the sake of consistency, we need to introduce a similar check

[ximinez]

Good catch. Fixed.

[ckeshava]

The data members flags::account_ and nflags::account_ always hold a valid instance of the Account class. These data members are not pointers or std::optional values.

Hence, env.le(account_) must always exist, isn't it? Are you envisioning a future modification to these flags and nflags classes, due to which a null pointer might be returned here?

[ximinez]

A valid instance of an Account does not guarantee that that account has been created / funded on the ledger. So even though the Account is valid, a null sle could easily be returned. Consider this test:

Env env{*this};
Account alice("alice");

env.require(flags(alice, asfRequireDest));
env.require(nflags(alice, asfRequireAuth));

That's a perfectly validly written test, but without this change, it'll dereference a null SLE and crash. With this change, the test will fail in the changed functions, but it won't crash.