Mockk，如何模拟在私有函数中使用的 JSONObject 构造函数

Question

using mockk, testImplementation "io.mockk:mockk:1.9.3"

having a class MetaData built through api fun from(intent: Intent?): MetaData?

class MetaData {

    @JvmField
    val rid: String
    ......

   private constructor(meta: JSONObject) {
        rid = meta.optString("RID", "")
    }

   companion object {

        @JvmStatic
        fun from(intent: Intent?): MetaData? {
            if (intent == null) {
                 return null
            }

            val metaJsonStr: String = intent.getStringExtra("meta") ?: return null
                   
            val rmeta = getMetaDataJson(metaJsonStr)
                ?: return null
                     
            return MetaData(meta)
        }
        
        private fun getMetaDataJson(json: String): JSONObject? {
            
            return try {
                JSONObject(json)
            } catch (e: JSONException) {
                System.out.println("+++ !!! 111 exp in getMetaDataJson(), $e")
                null
            } catch (e: NullPointerException) {
                System.out.println("+++ !!! 222 exp in getMetaDataJson(), $e")
                null
            }
        }
    }
}

would like to test the code path which throws JSONException and NullPointerException .

Have tried this test the and it can test the null path from intent.getStringExtra("meta")

@Test
    fun test_from_WhenCalledWithIntentWithNometa_ShouldReturnNull() {
        val intentMock: Intent = mockk<Intent>(relaxed = true)
        every { intentMock.getStringExtra(any()) } returns null
        val metaData = MetaData.from(intentMock)
        Assert.assertEquals(metaData, null)
    }

How to make this test to step into the getMetaDataJson(json) , I guess that needs to not mocking the Intent but the JSONObject constructor (how)?

Or is it possible to stub the fun getMetaDataJson(json: String) but no matter what the input is it should replace the input json string to some configured test data?

How to test the two exception path?

Answer 1

/**
 * Creates a new {@code JSONObject} with name/value mappings from the JSON
 * string.
 *
 * @param json a JSON-encoded string containing an object.
 * @throws JSONException if the parse fails or doesn't yield a {@code
 *     JSONObject}.
 */
public JSONObject(@NonNull String json) throws JSONException {
    this(new JSONTokener(json));
}

The JSONObject construct will throw an exception if the passed string is not valid. Just pass a random string like "This random: String" and you should get the JSONException .

Regarding the NullPointerException you should not guard for this exception since the constructor doesn't throw it.

Answer 2

You can try with Constructor mock . It's available from mockk 1.11.0