Danny Chia Danny Chia - 1 year ago 67
Java Question

Android unit testing - "logcat -c" is clearing logs more often than it's supposed to

I wrote some unit tests to check whether logging is working as intended. For example, here is one of the methods being tested:

// from my SampleObject class
public void configure(Context context) {

Log.d(TAG, "Configuration done.");

I want to flush LogCat before each test so that the logs from the previous test do not get picked up. To do that, I wrote a
method that is called from

private void clearLogs() throws Exception {
Runtime.getRuntime().exec("logcat -c");

public void setUp() throws Exception {
SampleObject mSampleObject = new SampleObject();

And here is my unit test:

public void testConfigure() throws Exception {
String LOG_CONFIGURATION_DONE = "Configuration done.";
boolean stringFound = false;
mSampleObject.configure(new MockContext());
Process process = Runtime.getRuntime().exec("logcat -d SampleObject:D *:S");
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(process.getInputStream()));
String line = "";
while ((line = bufferedReader.readLine()) != null) {
if (line.contains(LOG_CONFIGURATION_DONE)) {
stringFound = true;
assertTrue("Log message for configure() not found", stringFound);

The issue is that the log entry is cleared even though
is only called in
. The test works if I comment out
. Anyone have an idea what I'm doing wrong?

Answer Source

After several weeks, I've finally discovered the cause: logcat -c does not clear the logs immediately but takes several seconds to do so. However, the process appears from the test application's point of view. As a result, the test case is executed immediately afterwards and runs while the logs are still being cleared. Adding a short delay of two seconds resolved the problem.