Main difference to 6.1 / 6.2:

• testDumpingTaggedValueTopLevelAssoc(): instead of error we get empty string as result, which is still wrong.
• testDumpingTaggedValueTopLevelMultiLine(): instead of error we get empty string as result, which is still wrong.

If we can't have a comma after the last argument of a multi-line function call, I rather put the closing ) on the same line.
This also seems to be the convention in the rest of this code.

                $this->assertSame(
                    $expected,
                    $this->parser->parse(
                        $this->dumper->dump($expected, 10)),
                    $test['test']);

I'm a bit undecided about code style because it is already so inconsistent :)

So how do we bring this to the other branches once it is merged?

Added "[Yaml] " in the commit messages.
I don't know if there is any explicit convention, but seems better than nothing.

@donquixote the core team will then merge the 4.4 branch into the 5.4 branch, and so on.

We should standardize the use of local variables. Can we agree on something?
In most of the methods we can have $data and $expected, and then the rest can be done with nested calls, like this:

        $data = new TaggedValue('user', ['name' => 'jane']);
        $expected = '!user { name: jane }';
        $this->assertSame($expected, $this->dumper->dump($data));
        // If we want to keep the round trip test:
        $this->assertSameData($data, $this->parser->parse($expected, Yaml::PARSE_CUSTOM_TAGS));

Would be even nicer to work with data providers, but these also need to contain the parameters to send to dumper and parser (unless we drop the parser).
Or a method $this->assertRoundTrip($data, $expected);, but then again we need to pass the additional parameters, e.g. $this->assertRoundTrip($data, $expected, $inline, $indent, $dumperFlags, $parserFlags);

I am going to fix code style later as reported by fabbot.io.
But let's agree about other points:

• Standardize local vars.
• Standardize blank lines.
• Assert round trip or not, or only sometimes?

The PR is ready for another review, just saying :)
No need to get lost in the empty() question, I already replaced it.

Thank you @donquixote.

Oh no!
Two methods in DumperTest were lost when merging to 6.0 :(

testDumpingTaggedValueTopLevelAssoc()
testDumpingTaggedValueTopLevelMultiLine()

I know: they failed so I removed them, knowing you would rebase your other PR and resurrect them :)