tests: Set descriptors default based on compilation

Determines whether descriptors should be used based on whether the
--descriptor or --legacy-wallet option is set,
and the compiled support. If no option is set and both BDB and SQLite
are available, it defaults to legacy.

This is used to switch descriptor agnostic tests between descriptors and
legacy wallet.

Author: achow101

test/functional/test_framework/test_framework.py

@@ -186,15 +186,30 @@ def parse_args(self):
         parser.add_argument('--timeout-factor', dest="timeout_factor", type=float, default=1.0, help='adjust test timeouts by a factor. Setting it to 0 disables all timeouts')
 
         group = parser.add_mutually_exclusive_group()
-        group.add_argument("--descriptors", default=False, action="store_true",
+        group.add_argument("--descriptors", action='store_const', const=True,
                             help="Run test using a descriptor wallet", dest='descriptors')
-        group.add_argument("--legacy-wallet", default=False, action="store_false",
+        group.add_argument("--legacy-wallet", action='store_const', const=False,
                             help="Run test using legacy wallets", dest='descriptors')
 
         self.add_options(parser)
         self.options = parser.parse_args()
         self.options.previous_releases_path = previous_releases_path
 
+        config = configparser.ConfigParser()
+        config.read_file(open(self.options.configfile))
+        self.config = config
+
+        if self.options.descriptors is None:
+            # Prefer BDB unless it isn't available
+            if self.is_bdb_compiled():
+                self.options.descriptors = False
+            elif self.is_sqlite_compiled():
+                self.options.descriptors = True
+            else:
+                # If neither are compiled, tests requiring a wallet will be skipped and the value of self.options.descriptors won't matter
+                # It still needs to exist and be None in order for tests to work however.
+                self.options.descriptors = None
+
     def setup(self):
         """Call this method to start up the test framework object with options set."""
 
@@ -204,9 +219,8 @@ def setup(self):
 
         self.options.cachedir = os.path.abspath(self.options.cachedir)
 
-        config = configparser.ConfigParser()
-        config.read_file(open(self.options.configfile))
-        self.config = config
+        config = self.config
+
         fname_bitcoind = os.path.join(
             config["environment"]["BUILDDIR"],
             "src",