What is Mocking? .
Mocking
mockingunit testing
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I've actually used your first approach with quite some success, but in a slightly different ways that I think would solve some of your problems:
Keep the entire schema and scripts for creating it in source control so that anyone can create the current database schema after a check out. In addition, keep sample data in data files that get loaded by part of the build process. As you discover data that causes errors, add it to your sample data to check that errors don't re-emerge.
Use a continuous integration server to build the database schema, load the sample data, and run tests. This is how we keep our test database in sync (rebuilding it at every test run). Though this requires that the CI server have access and ownership of its own dedicated database instance, I say that having our db schema built 3 times a day has dramatically helped find errors that probably would not have been found till just before delivery (if not later). I can't say that I rebuild the schema before every commit. Does anybody? With this approach you won't have to (well maybe we should, but its not a big deal if someone forgets).
For my group, user input is done at the application level (not db) so this is tested via standard unit tests.
Loading Production Database Copy:
This was the approach that was used at my last job. It was a huge pain cause of a couple of issues:
- The copy would get out of date from the production version
- Changes would be made to the copy's schema and wouldn't get propagated to the production systems. At this point we'd have diverging schemas. Not fun.
Mocking Database Server:
We also do this at my current job. After every commit we execute unit tests against the application code that have mock db accessors injected. Then three times a day we execute the full db build described above. I definitely recommend both approaches.
You can get some information :
From Martin Fowler about Mock and Stub
Fake objects actually have working implementations, but usually take some shortcut which makes them not suitable for production
Stubs provide canned answers to calls made during the test, usually not responding at all to anything outside what's programmed in for the test. Stubs may also record information about calls, such as an email gateway stub that remembers the messages it 'sent', or maybe only how many messages it 'sent'.
Mocks are what we are talking about here: objects pre-programmed with expectations which form a specification of the calls they are expected to receive.
From xunitpattern:
Fake: We acquire or build a very lightweight implementation of the same functionality as provided by a component that the SUT depends on and instruct the SUT to use it instead of the real.
Stub : This implementation is configured to respond to calls from the SUT with the values (or exceptions) that will exercise the Untested Code (see Production Bugs on page X) within the SUT. A key indication for using a Test Stub is having Untested Code caused by the inability to control the indirect inputs of the SUT
Mock Object that implements the same interface as an object on which the SUT (System Under Test) depends. We can use a Mock Object as an observation point when we need to do Behavior Verification to avoid having an Untested Requirement (see Production Bugs on page X) caused by an inability to observe side-effects of invoking methods on the SUT.
Personally
I try to simplify by using : Mock and Stub. I use Mock when it's an object that returns a value that is set to the tested class. I use Stub to mimic an Interface or Abstract class to be tested. In fact, it doesn't really matter what you call it, they are all classes that aren't used in production, and are used as utility classes for testing.
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Best Answer
Prologue: If you look up the noun mock in the dictionary you will find that one of the definitions of the word is something made as an imitation.
At times you may want to distinguish between mocking as opposed to stubbing. There may be some disagreement about this subject but my definition of a stub is a "minimal" simulated object. The stub implements just enough behavior to allow the object under test to execute the test.
A mock is like a stub but the test will also verify that the object under test calls the mock as expected. Part of the test is verifying that the mock was used correctly.
To give an example: You can stub a database by implementing a simple in-memory structure for storing records. The object under test can then read and write records to the database stub to allow it to execute the test. This could test some behavior of the object not related to the database and the database stub would be included just to let the test run.
If you instead want to verify that the object under test writes some specific data to the database you will have to mock the database. Your test would then incorporate assertions about what was written to the database mock.