Output of my Scala refsol matches output of authors original refsol in Python. Being unable to read the description is not an issue.

It appears to me that the Scala solution is correct.

For Seq("B", "B", "A", "A", "A", "B", "A") I would expect:

• Pop "B", "B" from index 0 => Seq("A", "A", "A", "B", "A")
• Pop "A", "A", "A" from index 0 => Seq("B", "A")
• Nothing more to pop; return Seq("B", "A")

when I test the reference solution popBlocks(Seq("B", "B", "A", "A", "A", "B", "A")) => Seq("B", "A")

Do you expect something different? If so, what?

Just for completeness: you mean Scala tests, right?