Add a testing module for soil-query 🧪

[ogaclejapan]

We provide a testing package that enhances testability by introducing a mocking mechanism for executing query and mutation blocks. This capability enables the execution of tests without the need for actual API communication, thereby increasing test independence.

@Test
fun testQuery() = runTest {
    val client = SwrCache(
        policy = SwrCachePolicy(
            coroutineScope = backgroundScope,
            mainDispatcher = UnconfinedTestDispatcher(testScheduler)
        )
    )
    val testClient = client.test().apply {
        mock(ExampleQueryKey.Id) {
            "Hello, World!"
        }
    }
    val key = ExampleQueryKey()
    val query = testClient.getQuery(key).also { it.launchIn(backgroundScope) }
    query.test()
    assertEquals("Hello, World!", query.state.value.data)
}