lib: xapian-db/config: more tests

...and xapian-db gets a small API update, update store as well.

lib/mu-xapian-db.cc

@@ -90,8 +90,10 @@ make_db(const std::string& db_path, Flavor flavor)
 		return Xapian::WritableDatabase(db_path, Xapian::DB_OPEN);
 	case Flavor::CreateOverwrite:
 		return Xapian::WritableDatabase(db_path, Xapian::DB_CREATE_OR_OVERWRITE);
+		/* LCOV_EXCL_START*/
 	default:
 		throw std::logic_error("unknown flavor");
+		/* LCOV_EXCL_STOP*/
 	}
 }
 
@@ -104,3 +106,43 @@ XapianDb::XapianDb(const std::string& db_path, Flavor flavor) :
 
 	mu_debug("created {} / {}", flavor, *this);
 }
+
+
+
+
+#ifdef BUILD_TESTS
+/*
+ * Tests.
+ *
+ */
+
+#include "utils/mu-test-utils.hh"
+#include "config.h"
+#include "mu-store.hh"
+
+static void
+test_errors()
+{
+	allow_warnings();
+
+	TempDir tdir;
+	auto store = Store::make_new(tdir.path(), MU_TESTMAILDIR2);
+	assert_valid_result(store);
+	g_assert_true(store->empty());
+
+	XapianDb xdb(tdir.path(), Flavor::ReadOnly);
+	g_assert_true(xdb.read_only());
+
+	g_assert_false(!!xdb.delete_document("Boo"));
+}
+
+int
+main(int argc, char* argv[])
+{
+	mu_test_init(&argc, &argv);
+
+	g_test_add_func("/xapian-db/errors", test_errors);
+
+	return g_test_run();
+}
+#endif /*BUILD_TESTS*/