general: move most core tests inside my.core.tests package

- distributes tests alongside the package, might be convenient for package users
- removes some weird indirection (e.g. dummy test files improting tests from modules)
- makes the command line for tests cleaner (e.g. no need to remember to manually add files to tox.ini)
- tests automatically covered by mypy (so makes mypy runs cleaner and ultimately better coverage)

The (vague) convention is

- tests/somemodule.py -- testing my.core.somemodule, contains tests directly re
- tests/test_something.py -- testing a specific feature, e.g. test_get_files.py tests get_files methon only

tests/sqlite.py

@@ -1,66 +0,0 @@
-from pathlib import Path
-import shutil
-import sqlite3
-from tempfile import TemporaryDirectory
-
-
-from my.core.sqlite import sqlite_connect_immutable, sqlite_copy_and_open
-
-
-def test_sqlite_read_with_wal(tmp_path: Path) -> None:
-    db = tmp_path / 'db.sqlite'
-    # write a bit
-    with sqlite3.connect(str(db)) as conn:
-        conn.execute('CREATE TABLE testtable (col)')
-        for i in range(5):
-            conn.execute('INSERT INTO testtable (col) VALUES (?)', str(i))
-
-    # write more in WAL mode
-    with sqlite3.connect(str(db)) as conn_db:
-        conn.execute('PRAGMA journal_mode=wal;')
-        for i in range(5, 10):
-            conn_db.execute('INSERT INTO testtable (col) VALUES (?)', str(i))
-        conn_db.execute('COMMIT')
-
-        # make sure it has unflushed stuff in wal
-        wals = list(db.parent.glob('*-wal'))
-        assert len(wals) == 1
-
-        ## now run the tests in separate process to ensure there is no potential for reusing sqlite connections or something
-        from concurrent.futures import ProcessPoolExecutor as Pool
-        with Pool(1) as pool:
-            # merely using it for ctx manager..
-            pool.submit(_test_do_copy         , db).result()
-            pool.submit(_test_do_immutable    , db).result()
-            pool.submit(_test_do_copy_and_open, db).result()
-            pool.submit(_test_open_asis       , db).result()
-
-
-def _test_do_copy(db: Path) -> None:
-    # from a copy without journal can only read previously committed stuff
-    with TemporaryDirectory() as tdir:
-        cdb = Path(tdir) / 'dbcopy.sqlite'
-        shutil.copy(db, cdb)
-        with sqlite3.connect(str(cdb)) as conn_copy:
-            assert len(list(conn_copy.execute('SELECT * FROM testtable'))) == 5
-        conn_copy.close()
-
-
-def _test_do_immutable(db: Path) -> None:
-    # in readonly mode doesn't touch
-    with sqlite_connect_immutable(db) as conn_imm:
-        assert len(list(conn_imm.execute('SELECT * FROM testtable'))) == 5
-    conn_imm.close()
-
-
-def _test_do_copy_and_open(db: Path) -> None:
-    with sqlite_copy_and_open(db) as conn_mem:
-        assert len(list(conn_mem.execute('SELECT * FROM testtable'))) == 10
-    conn_mem.close()
-
-
-def _test_open_asis(db: Path) -> None:
-    # NOTE: this also works... but leaves some potential for DB corruption
-    with sqlite3.connect(str(db)) as conn_db_2:
-        assert len(list(conn_db_2.execute('SELECT * FROM testtable'))) == 10
-    conn_db_2.close()