Test new syntax in 3.10

[alexmojaki]

https://docs.python.org/3/whatsnew/3.10.html

• Pattern matching. One quick way is to add this so that test_sys_modules tests it:

      try:
        import test.test_patma
      except ImportError:
        pass

This works, which suggests that no fixes are needed. Slightly less crude would be making a proper fixture file. Obviously a targeted test would be ideal.

• Parenthesised context managers.

[alexmojaki]

ast.match_case nodes don't have lineno/col_offset, so ASTText doesn't support them, but ASTTokens does:

import ast
import asttokens

source = """
match foo:
    case bar:
        print(spam)
"""

atext = asttokens.ASTText(source)
print(ast.dump(atext.tree, include_attributes=True, indent=4))

match_case = atext.tree.body[0].cases[0]
assert atext.get_text(match_case) == ''
assert atext.asttokens.get_text(match_case) == """\
    case bar:
        print(spam)"""

[alexmojaki]

Added a bit of testing in #102 but didn't check all the match-related AST nodes and didn't address the above.