To pull the discussion out of the PR:

The implicit(*) object to string conversion $this->assertEquals('08:00', $clock) is a magic trick in PHP, but we currently have no concept (concept exercise) for students to learn about this. So for now we should do at least one of these:

• Explain the magic in the stub (a link to the PHP docs Stringable interface may be enough?)
• Explain the magic in instructions.append.md (like above)
• Avoid the magic and explicitly call the method as done before $this->assertEquals('08:00', $clock->__toString())
• Invoke the magic explicitly by converting the object to a string $this->assertEquals('08:00', (string)$clock)

I'd prefer having a DocBlock above __toString() in the students stub pointing at Stringable interface in PHP docs and an explicit conversion (string)$clock in the tests. This allows us to use the magic in the tests and helps students find all required information about what __toString() is.

Opinions? @tomasnorre @homersimpsons

(*) Implicit here means: PHPUnit does the conversion instead of us, so it is invisible for students.

I'd prefer having a DocBlock above __toString() in the students stub pointing at Stringable interface in PHP docs and an explicit conversion (string)$clock in the tests. This allows us to use the magic in the tests and helps students find all required information about what __toString() is.

I'm perfectly fine with this. I should not forget we are in a learning scenario.

I agree that we should not let the PHP's implicit cast to string. If we want to keep it I prefer to go with an explicit cast (string). I think that the explanation in the stub has more chances to be read so I would vote to have at least this one.

I'm fine with going more in depth (or repeating the source comment) in the instructions.append.md.

Thanks everyone for opinions. So we go with (string)$clock and a comment in the students stub. I'd leave in-depth descriptions for the time adding a concept for magic methods.

@tomasnorre Would you be so kind to update the PR?