function assertReasonHelper(checker, one, two, reason) {
      chai.assert.equal(checker.canConnectWithReason(one, two), reason);
      // Order should not matter.
      chai.assert.equal(checker.canConnectWithReason(two, one), reason);
    }
Assert that the given connections pass or fail safety checks for the
given reason, and in both orders.
@param {!Blockly.IConnectionChecker} checker The connection checker
    object under test.
@param {!Blockly.Connection} one The first connection.
@param {!Blockly.Connection} two The second connection.
@param {number} reason The expected return value of
    `canConnectWithReason`.