diff --git a/test/tap/groups/mysql84/env.sh b/test/tap/groups/mysql84/env.sh
index 66301acc3..d35f807c9 100755
--- a/test/tap/groups/mysql84/env.sh
+++ b/test/tap/groups/mysql84/env.sh
@@ -1,8 +1,14 @@
-# Legacy Test Group Environment
-# Defines the primary targets for tests that expect a generic MySQL or PGSQL backend.
+# MySQL 8.4 Test Group Environment
 
 export DEFAULT_MYSQL_INFRA="infra-mysql84"
 
+# Source infra .env to export TAP test variables (TAP_MYSQL8_BACKEND_HG, etc.)
+# Uses WORKSPACE (always set in CI) to avoid shell-specific BASH_SOURCE
+if [ -n "${WORKSPACE}" ]; then
+    _INFRA_ENV="${WORKSPACE}/test/infra/${DEFAULT_MYSQL_INFRA}/.env"
+    [ -f "${_INFRA_ENV}" ] && . "${_INFRA_ENV}"
+fi
+
 # Path to RESTAPI test scripts inside ProxySQL container
 # The setup-infras.bash hook copies scripts to the ProxySQL data directory
 export REGULAR_INFRA_DATADIR="/var/lib/proxysql"
diff --git a/test/tap/tests/reg_test_4935-caching_sha2-t.env b/test/tap/tests/reg_test_4935-caching_sha2-t.env
index 4036e7d02..99f515318 100644
--- a/test/tap/tests/reg_test_4935-caching_sha2-t.env
+++ b/test/tap/tests/reg_test_4935-caching_sha2-t.env
@@ -1,2 +1 @@
-TAP_MYSQL8_BACKEND_HG=30
 TAP_NUM_CLIENT_THREADS=4
diff --git a/test/tap/tests/test_auth_methods-t.env b/test/tap/tests/test_auth_methods-t.env
index 73c1bdfe4..7cd8c3bd8 100644
--- a/test/tap/tests/test_auth_methods-t.env
+++ b/test/tap/tests/test_auth_methods-t.env
@@ -1,4 +1,3 @@
 TAP_MYSQLUSERNAME=root
 
-TAP_MYSQL8_BACKEND_HG=30
 TAP_NUM_CLIENT_THREADS=4
diff --git a/test/tap/tests/test_read_only_actions_offline_hard_servers-t.cpp b/test/tap/tests/test_read_only_actions_offline_hard_servers-t.cpp
index 5f0762d6e..3d7862320 100644
--- a/test/tap/tests/test_read_only_actions_offline_hard_servers-t.cpp
+++ b/test/tap/tests/test_read_only_actions_offline_hard_servers-t.cpp
@@ -29,6 +29,19 @@ using std::pair;
 
 const uint32_t SYNC_TIMEOUT = 10;
 
+// Writer and reader hostgroups — read from TAP_MYSQL8_BACKEND_HG env var.
+// Defaults to 0/1 for backward compatibility with legacy infra.
+static int WHG = 0;
+static int RHG = 1;
+
+static void init_hostgroups() {
+	const char* hg_env = getenv("TAP_MYSQL8_BACKEND_HG");
+	if (hg_env) {
+		WHG = atoi(hg_env);
+		RHG = WHG + 1;
+	}
+}
+
 using mysql_server_tuple = std::tuple<int,std::string,int,int,std::string,int,int,int,int,int,int,std::string>;
 using replication_hostgroups_tuple = std::tuple<int,int,std::string>;
 
@@ -198,11 +211,11 @@ int test_scenario_1(MYSQL* proxy_admin, const CommandLine& cl) {
 	MYSQL* dummy_mysqldb = NULL;
 	
 	const std::vector<mysql_server_tuple> insert_mysql_servers_values {
-		std::make_tuple(0, cl.mysql_host, cl.mysql_port, 12, "ONLINE", 1, 1, 1000, 300, 1, 200, "") // this server has read_only value 0 (writer)
+		std::make_tuple(WHG, cl.mysql_host, cl.mysql_port, 12, "ONLINE", 1, 1, 1000, 300, 1, 200, "") // this server has read_only value 0 (writer)
 	};
 
 	const std::vector<replication_hostgroups_tuple> insert_replication_hostgroups_values {
-		std::make_tuple(0, 1, "read_only") 
+		std::make_tuple(WHG, RHG, "read_only")
 	};
 
 	// cleaning old records
@@ -351,11 +364,11 @@ int test_scenario_2(MYSQL* proxy_admin, const CommandLine& cl) {
 	MYSQL* dummy_mysqldb = NULL;
 
 	const std::vector<mysql_server_tuple> insert_mysql_servers_values {
-		std::make_tuple(1, cl.mysql_host, cl.mysql_port, 12, "ONLINE", 1, 1, 1000, 300, 1, 200, "") // this server has read_only value 0 (writer)
+		std::make_tuple(RHG, cl.mysql_host, cl.mysql_port, 12, "ONLINE", 1, 1, 1000, 300, 1, 200, "") // this server has read_only value 0 (writer)
 	};
 
 	const std::vector<replication_hostgroups_tuple> insert_replication_hostgroups_values {
-		std::make_tuple(0, 1, "read_only") 
+		std::make_tuple(WHG, RHG, "read_only")
 	};
 
 	// cleaning old records
@@ -587,6 +600,9 @@ int main(int, char**) {
 		return EXIT_FAILURE;
 	}
 
+	init_hostgroups();
+	diag("Using hostgroups: WHG=%d, RHG=%d", WHG, RHG);
+
 	plan(9+9);
 
 	MYSQL* proxy_admin = mysql_init(NULL);
diff --git a/test/tap/tests/test_sqlite3_pass_exts-t.env b/test/tap/tests/test_sqlite3_pass_exts-t.env
index ed9226ab2..42defa00f 100644
--- a/test/tap/tests/test_sqlite3_pass_exts-t.env
+++ b/test/tap/tests/test_sqlite3_pass_exts-t.env
@@ -1,2 +1 @@
 TAP_MYSQLUSERNAME=root
-TAP_MYSQL8_BACKEND_HG=30