Test: Fix test_unsupported_queries for isolated CI environment

Use REGULAR_INFRA_DATADIR environment variable to locate the
load_data_local_datadir files in the shared volume when running
in containerized CI environment. Falls back to cl.workdir for
local testing.

test/tap/tests/test_unsupported_queries-t.cpp

@@ -170,9 +170,10 @@ using mysql_res_row = std::vector<std::string>;
 void helper_test_load_data_local_infile(
 	const CommandLine& cl, MYSQL* proxysql, int exp_err=0, bool test_for_success=true
 ) {
-	std::string datafile {
-		std::string { cl.workdir } + "load_data_local_datadir/insert_data.txt"
-	};
+	const char* d_env = getenv("REGULAR_INFRA_DATADIR");
+	std::string datafile = (d_env ? std::string(d_env) + "/load_data_local_datadir/insert_data.txt"
+	                              : std::string(cl.workdir) + "load_data_local_datadir/insert_data.txt");
+	diag("Data file path: %s", datafile.c_str());
 
 	bool table_prep_success = true;
 
@@ -363,9 +364,10 @@ void test_failing_load_data_local_infile(
 	const CommandLine& cl, MYSQL* proxysql, int exp_err=0, bool test_for_success=true
 ) {
 	// Supply an invalid file
-	std::string datafile {
-		std::string { cl.workdir } + "load_data_local_datadir/non_existing_file.txt"
-	};
+	const char* d_env = getenv("REGULAR_INFRA_DATADIR");
+	std::string datafile = (d_env ? std::string(d_env) + "/load_data_local_datadir/non_existing_file.txt"
+	                              : std::string(cl.workdir) + "load_data_local_datadir/non_existing_file.txt");
+	diag("Data file path: %s", datafile.c_str());
 
 	bool table_prep_success = true;
 
@@ -500,6 +502,25 @@ int main(int argc, char** argv) {
 		return -1;
 	}
 
+	// Verbose test header
+	diag("================================================================================");
+	diag("Test: test_unsupported_queries-t");
+	diag("================================================================================");
+	diag("This test verifies that unsupported queries return the expected error codes,");
+	diag("and that conditionally-enabled queries work correctly when enabled/disabled.");
+	diag("");
+	diag("Test scenarios:");
+	diag("  - Unsupported queries (LOAD DATA LOCAL INFILE) should fail with error 1047");
+	diag("  - Conditionally enabled queries should work when enabled");
+	diag("  - Conditionally enabled queries should fail when disabled");
+	diag("");
+	diag("Connection parameters:");
+	diag("  - Host: %s", cl.host);
+	diag("  - Port: %d", cl.port);
+	diag("  - Admin Port: %d", cl.admin_port);
+	diag("================================================================================");
+	diag("");
+
 	// perform a different connection per query
 	for (const auto& unsupported_query : unsupported_queries) {
 		MYSQL* proxysql_mysql = mysql_init(NULL);