Improve FORM test coverage

[greenc-FNAL]

• Improve test coverage of FORM code
• Address Improve test coverage of FORM code #333 (review)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff             @@
##             main     #340      +/-   ##
==========================================
+ Coverage   80.39%   81.39%   +0.99%     
==========================================
  Files         127      127              
  Lines        3102     3102              
  Branches      547      547              
==========================================
+ Hits         2494     2525      +31     
+ Misses        381      359      -22     
+ Partials      227      218       -9     

Flag	Coverage Δ
unittests	81.39% <ø> (+0.99%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
form/util/factories.hpp	45.00% <ø> (ø)

... and 10 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e71e70e...19b1031. Read the comment docs.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[aolivier23]

Looks good, thanks. I don't yet understand what the inline does.

[wwuoneway]

inline here can help achieves linkage/safe w.r.t. One Definition Rule (ODR).
Looks good to me.

[knoepfel]

Looks good, thanks. I don't yet understand what the inline does.

@aolivier23, a free function should not be defined in a header file as it will create multiple definitions in separate translation units that, when linked together, will result in multiple definitions in the same library. To avoid this problem, the free function should be declared in the header file only. Or, the function definition can be marked inline, and that's an indication to the compiler that the function definition should be treated as an inline definition that would be expanded at the function's call sites.