Confusing failures when testing datasources via the console in domain mode on EAP

Issue

• console shows errors similar to:

Failed to create JDBC connection.
An internal error occured.
details

• details tells of failing composite operation

Unexpected HTTP response: 500

Request
{
    "address" => [],
    "operation" => "composite",
    "steps" => [
        {
            "operation" => "test-connection-in-pool",
            "address" => [
                ("host" => "master"),
                ("server" => "server-one"),
                ("subsystem" => "datasources"),
                ("data-source" => "ExampleDS")
            ]
        },
        {
            "operation" => "test-connection-in-pool",
            "address" => [
                ("host" => "master"),
                ("server" => "server-two"),
                ("subsystem" => "datasources"),
                ("data-source" => "ExampleDS")
            ]
        }
    ]
}

Response

Internal Server Error
{
    "outcome" => "failed",
    "result" => {
        "step-1" => {
            "outcome" => "failed",
            "result" => [true],
            "rolled-back" => true
        },
        "step-2" => {
            "outcome" => "failed",
            "failure-description" => "JBAS010440: failed to invoke operation: JBAS010447: Connection is not valid",
            "rolled-back" => true
        }
    },
    "failure-description" => "JBAS010839: Operation failed or was rolled back on all servers.",
    "rolled-back" => true,
    "server-groups" => {"main-server-group" => {"host" => {"master" => {
        "server-one" => {"response" => {
            "outcome" => "failed",
            "result" => {"step-1" => {
                "outcome" => "failed",
                "result" => [true],
                "rolled-back" => true
            }},
            "failure-description" => "JBAS014654: Composite operation was rolled back",
            "rolled-back" => true
        }},
        "server-two" => {"response" => {
            "outcome" => "failed",
            "result" => {"step-1" => {
                "outcome" => "failed",
                "failure-description" => "JBAS010440: failed to invoke operation: JBAS010447: Connection is not valid",
                "rolled-back" => true
            }},
            "failure-description" => {"JBAS014653: Composite operation failed and was rolled back. Steps that failed:" => {"Operation step-1" => "JBAS010440: failed to invoke operation: JBAS010447: Connection is not valid"}},
            "rolled-back" => true
        }}
    }}}}
}