Dynamic MockApi for testing

[TarikGul]

Proposed Change or Idea

Create a more dynamic mockApi for our test suite. An example would be to turn the existing mockApi object, that has hardcoded values, into a function that would take a set of default key values and a set of option key values as it's parameters. I think this could be useful in having more readable testing, and would encourage a wider range of testing for edge cases.

For example something similar to this could work.

export const mockApi = (options, default=DEFAULT_POLKADOT_API_DATA) => {
    return {
        ...
        derive: {
            chain: {
		getHeader: options.derive.chain.getHeader ? options.derive.chain.getHeader : default.derive.chain.getHeader ,
		getBlock: options.derive.chain.getBlock ? options.derive.chain.getBlock : default.derive.chain.getBlock ,
	    },
	},
        ....
    }
}

This is how we currently get around an edge case by overriding values in the mockApi object

/**
 * CURRENT
 */               
it('Return an error with a null calcFee when perByte is undefined', async () => {
    mockApi.consts.transactionPayment.transactionByteFee = (undefined as unknown) as BalanceOf &
        AugmentedConst<'promise'>;

    const configuredBlocksService = new BlocksService(mockApi);

    // fetchBlock options
    const options = {
        eventDocs: true,
        extrinsicDocs: true,
        checkFinalized: false,
        queryFinalizedHead: false,
        omitFinalizedTag: false,
    };

    const response = sanitizeNumbers(
        await configuredBlocksService.fetchBlock(
            blockHash789629,
            options
        )
    );

    const responseObj: ResponseObj = JSON.parse(
        JSON.stringify(response)
    );

    // Revert mockApi back to its original setting that was changed above.
    mockApi.consts.transactionPayment.transactionByteFee = polkadotRegistry.createType(
        'Balance',
        1000000
    ) as BalanceOf & AugmentedConst<'promise'>;

    expect(responseObj.extrinsics[3].info).toEqual({
        error: 'Fee calculation not supported for 16#polkadot',
    });
});

This is how the proposed idea would look like

/**
 * PROPOSED
 */
it('Return an error with a null calcFee when perByte is undefined', async () => {
    const calcFeeOptions = {
        consts: {
            transactionPayment: {
                transactionByteFee = (undefined as unknown) as BalanceOf & AugmentedConst<'promise'>;
            }    
        }
    }

    const calcFeePerByteMockApi = mockApi(calcFeeOptions);
    
    const calcFeePerByteBlocksService = new BlocksService(calcFeePerByteMockApi);
    
    // fetchBlock options
    const options = {
        eventDocs: true,
        extrinsicDocs: true,
        checkFinalized: false,
        queryFinalizedHead: false,
        omitFinalizedTag: false,
    };

    const response = sanitizeNumbers(
        await calcFeePerByteBlocksService.fetchBlock(
            blockHash789629,
            options
        )
    );
    
    const responseObj: ResponseObj = JSON.parse(
        JSON.stringify(response)
    );

    expect(responseObj.extrinsics[3].info).toEqual({
        error: 'Fee calculation not supported for 16#polkadot',
    });
});

Alternatives

None I have thought of yet.

Additional Information

I think this could be a great way to organize the testing code more, and could be an enhancement for readability.

[dvdplm]

So essentially this would allow us to skip resetting the value(s) under test; instead the mocks automatically use the defaults unless overridden. Did I get that right? Sounds like a good QoL improvement.

[TarikGul]

Yup exactly, QoL improvement would definitely be the proper term. It would definitely be a large PR, but I think come the future it would encourage wider test coverage, and cleaner code.

[emostov]

Maybe related: https://kulshekhar.github.io/ts-jest/docs/guides/test-helpers

[TarikGul]

#702 closes this issue, as we have moved the mockApi testing structure to integrate with a historicApi. The way I implemented it is similar to the above.