Refactor tests

Organize tests into subdirectories and use a new makefile that scans
.sby files and allows selecting tests by mode, engine, solver and/or
subdirectory. Automatically skips tests that use engines/solvers that
are not found in the PATH.

See `cd tests; make help` for a description of supported make targets.

tests/make/collect_tests.py

@@ -0,0 +1,47 @@
+from pathlib import Path
+import re
+
+tests = []
+checked_dirs = []
+
+SAFE_PATH = re.compile(r"^[a-zA-Z0-9_./]*$")
+
+def collect(path):
+    # don't pick up any paths that need escaping nor any sby workdirs
+    if not SAFE_PATH.match(str(path)) or (path / "config.sby").exists():
+        return
+
+    checked_dirs.append(path)
+    for entry in path.glob("*.sby"):
+        filename = str(entry)
+        if not SAFE_PATH.match(filename):
+            continue
+        if not re.match(r"^[a-zA-Z0-9_./]*$", filename):
+            print(f"skipping {filename!r}, use only [a-zA-Z0-9_./] in filenames")
+            continue
+        tests.append(entry)
+    for entry in path.glob("*"):
+        if entry.is_dir():
+            collect(entry)
+
+
+collect(Path("."))
+
+out_file = Path("make/rules/collect.mk")
+out_file.parent.mkdir(exist_ok=True)
+
+with out_file.open("w") as output:
+
+
+    for checked_dir in checked_dirs:
+        print(f"{out_file}: {checked_dir}", file=output)
+
+    for test in tests:
+        print(f"make/rules/test/{test}.mk: {test}", file=output)
+        for ext in [".sh", ".py"]:
+            script_file = test.parent / (test.stem + ext)
+            if script_file.exists():
+                print(f"make/rules/test/{test}.mk: {script_file}", file=output)
+        print(f"make/rules/test/{test}.mk: make/test_rules.py", file=output)
+    for test in tests:
+        print(f"-include make/rules/test/{test}.mk", file=output)