When TestRPC and Geth throw, they behave in a different manner. This Gist is an example on how to cover such a situation.

expected_exception_testRPC_and_geth.js

"use strict";

/**
 * @param {!Function.<!Promise>} action.
 * @param {!Number | !string | !BigNumber} gasToUse.
 * @returns {!Promise} which throws unless it hit a valid error.
 */
module.exports = function expectedExceptionPromise(action, gasToUse) {
    return new Promise(function (resolve, reject) {
            try {
                resolve(action());
            } catch(e) {
                reject(e);
            }
        })
        .then(function (txObj) {
            return typeof txObj === "string" 
                ? web3.eth.getTransactionReceiptMined(txObj) // regular tx hash
                : typeof txObj.receipt !== "undefined"
                    ? txObj.receipt // truffle-contract function call
                    : typeof txObj.transactionHash === "string"
                        ? web3.eth.getTransactionReceiptMined(txObj.transactionHash) // deployment
                        : txObj; // Unknown last case
        })
        .then(
            function (receipt) {
                // We are in Geth
                if (typeof receipt.status !== "undefined") {
                    // Byzantium
                    assert.strictEqual(parseInt(receipt.status), 0, "should have reverted");
                } else {
                    // Pre Byzantium
                    assert.equal(receipt.gasUsed, gasToUse, "should have used all the gas");
                }
            },
            function (e) {
                if ((e + "").indexOf("invalid JUMP") > -1 ||
                        (e + "").indexOf("out of gas") > -1 ||
                        (e + "").indexOf("invalid opcode") > -1 ||
                        (e + "").indexOf("revert") > -1) {
                    // We are in TestRPC
                } else if ((e + "").indexOf("please check your gas amount") > -1) {
                    // We are in Geth for a deployment
                } else {
                    throw e;
                }
            }
        );
    };

Or in a .then() promise:

it("should not be possible to do something invalid", function () {

    return MyContract.new({ from: accounts[0] })
        .then(function (newMyContract) {
            return extensions.expectedExceptionPromise(function () {
                    return newMyContract.myFunction("invalidParam1",
                        { from: accounts[0], gas: 3000000 });
                }, 3000000);
        })

});

Great script, thanks!

One question:
Why don't you rethrow exception in lines 19 and 21?

@xavierlepretre amazing, thanks. I think there's a bug.

Line 18 might always evaluate to true.
Boolean("anything-bla-bla-bla".indexOf('invalid JUMP')) == true

I believe this will successfully cause tests to pass in the cases where an exception occurs, however it will not cause tests to fail in the event that an exception does not occur, which is different from the behaviour I expected.

This can be rectified on line 23 by replacing throw e with assert.isTrue(false) .