mockk, get error when using mockkstatic for stub static function

Question

using io.mockk 1.11.0

having some class with @JvmStatic function

class LogUtil {
    @JvmStatic
    fun logData(jsonStr: String) {
        val jsonObj = getDataJson(jsonStr)
        if (jsonObj == null) {
            Log.e("+++", "+++ wrong json")
        }
        // ......
    }
}

data util

class DataUtil {
    @JvmStatic
    fun getDataJson(json: String): JSONObject? {
        return try {
            JSONObject(json)
        } catch (e: Exception) {
            null
        }
    }
}

The test is to verify the Log.e(...) is called when a null is returned from getDataJson().

@Test
fun test_() {

    io.mockk.mockkStatic(android.utils.Log::class)
    io.mockk.mockkStatic(DataUtil::class)
    every { DataUtil.getDataJson(any()) } returns null  //<== error points to this line

    LogUtil.logData("{key: value}")

    verify(exactly = 1) { android.utils.Log.e("+++", any()) }
    
}

got error

io.mockk.MockKException: Failed matching mocking signature for
left matchers: [any()]

if change to every { DataUtil.getDataJson("test string") } returns null, it will get error

MockKException: Missing mocked calls inside every { ... } block: make sure the object inside the block is a mock

How to use mockkStatic for a @JvmStatic unction?

Answer 1

The use of mockkStatic is correct, but DataUtil is not static.

If your code is kotlin, must use object instead class:

object DataUtil { .. } object LogUtil { .. }

PD: Use unmockkStatic in @After method for avoid side effects that may affect other test.