I am trying to create some JUnit tests for a method that requires user input. The method under test looks somewhat like the following method:
public static int testUserInput() {
Scanner keyboard = new Scanner(System.in);
System.out.println("Give a number between 1 and 10");
int input = keyboard.nextInt();
while (input < 1 || input > 10) {
System.out.println("Wrong number, try again.");
input = keyboard.nextInt();
}
return input;
}
Is there a possible way to automatically pass the program an int instead of me or someone else doing this manually in the JUnit test method? Like simulating the user input?
You can replace System.in with you own stream by calling System.setIn(InputStream in).
InputStream can be a byte array:
InputStream sysInBackup = System.in; // backup System.in to restore it later
ByteArrayInputStream in = new ByteArrayInputStream("My string".getBytes());
System.setIn(in);
// do your thing
// optionally, reset System.in to its original
System.setIn(sysInBackup);
Different approach can be make this method more testable by passing IN and OUT as parameters:
public static int testUserInput(InputStream in,PrintStream out) {
Scanner keyboard = new Scanner(in);
out.println("Give a number between 1 and 10");
int input = keyboard.nextInt();
while (input < 1 || input > 10) {
out.println("Wrong number, try again.");
input = keyboard.nextInt();
}
return input;
}
To test drive your code, you should create a wrapper for system input/output functions. You can do this using dependency injection, giving us a class that can ask for new integers:
public static class IntegerAsker {
private final Scanner scanner;
private final PrintStream out;
public IntegerAsker(InputStream in, PrintStream out) {
scanner = new Scanner(in);
this.out = out;
}
public int ask(String message) {
out.println(message);
return scanner.nextInt();
}
}
Then you can create tests for your function, using a mock framework (I use Mockito):
#Test
public void getsIntegerWhenWithinBoundsOfOneToTen() throws Exception {
IntegerAsker asker = mock(IntegerAsker.class);
when(asker.ask(anyString())).thenReturn(3);
assertEquals(getBoundIntegerFromUser(asker), 3);
}
#Test
public void asksForNewIntegerWhenOutsideBoundsOfOneToTen() throws Exception {
IntegerAsker asker = mock(IntegerAsker.class);
when(asker.ask("Give a number between 1 and 10")).thenReturn(99);
when(asker.ask("Wrong number, try again.")).thenReturn(3);
getBoundIntegerFromUser(asker);
verify(asker).ask("Wrong number, try again.");
}
Then write your function that passes the tests. The function is much cleaner since you can remove the asking/getting integer duplication and the actual system calls are encapsulated.
public static void main(String[] args) {
getBoundIntegerFromUser(new IntegerAsker(System.in, System.out));
}
public static int getBoundIntegerFromUser(IntegerAsker asker) {
int input = asker.ask("Give a number between 1 and 10");
while (input < 1 || input > 10)
input = asker.ask("Wrong number, try again.");
return input;
}
This may seem like overkill for your small example, but if you are building a larger application developing like this can payoff rather quickly.
One common way to test similar code would be to extract a method that takes in a Scanner and a PrintWriter, similar to this StackOverflow answer, and test that:
public void processUserInput() {
processUserInput(new Scanner(System.in), System.out);
}
/** For testing. Package-private if possible. */
public void processUserInput(Scanner scanner, PrintWriter output) {
output.println("Give a number between 1 and 10");
int input = scanner.nextInt();
while (input < 1 || input > 10) {
output.println("Wrong number, try again.");
input = scanner.nextInt();
}
return input;
}
Do note that you won't be able to read your output until the end, and you'll have to specify all of your input up front:
#Test
public void shouldProcessUserInput() {
StringWriter output = new StringWriter();
String input = "11\n" // "Wrong number, try again."
+ "10\n";
assertEquals(10, systemUnderTest.processUserInput(
new Scanner(input), new PrintWriter(output)));
assertThat(output.toString(), contains("Wrong number, try again.")););
}
Of course, rather than creating an overload method, you could also keep the "scanner" and "output" as mutable fields in your system under test. I tend to like keeping classes as stateless as possible, but that's not a very big concession if it matters to you or your coworkers/instructor.
You might also choose to put your test code in the same Java package as the code under test (even if it's in a different source folder), which allows you to relax the visibility of the two parameter overload to be package-private.
I managed to find a simpler way. However, you have to use external library System.rules by #Stefan Birkner
I just took the example provided there, I think it couldn't have gotten more simpler:
import java.util.Scanner;
public class Summarize {
public static int sumOfNumbersFromSystemIn() {
Scanner scanner = new Scanner(System.in);
int firstSummand = scanner.nextInt();
int secondSummand = scanner.nextInt();
return firstSummand + secondSummand;
}
}
Test
import static org.junit.Assert.*;
import static org.junit.contrib.java.lang.system.TextFromStandardInputStream.*;
import org.junit.Rule;
import org.junit.Test;
import org.junit.contrib.java.lang.system.TextFromStandardInputStream;
public class SummarizeTest {
#Rule
public final TextFromStandardInputStream systemInMock
= emptyStandardInputStream();
#Test
public void summarizesTwoNumbers() {
systemInMock.provideLines("1", "2");
assertEquals(3, Summarize.sumOfNumbersFromSystemIn());
}
}
The problem however in my case my second input has spaces and this makes the whole input stream null!
You might start by extracting out the logic that retrieves the number from the keyboard into its own method. Then you can test the validation logic without worrying about the keyboard. In order to test the keyboard.nextInt() call you may want to consider using a mock object.
I have fixed the problem about read from stdin to simulate a console...
My problems was I'd like try write in JUnit test the console to create a certain object...
The problem is like all you say : How Can I write in the Stdin from JUnit test?
Then at college I learn about redirections like you say System.setIn(InputStream) change the stdin filedescriptor and you can write in then...
But there is one more proble to fix... the JUnit test block waiting read from your new InputStream, so you need create a thread to read from the InputStream and from JUnit test Thread write in the new Stdin... First you have to write in the Stdin because if you write later of create the Thread to read from stdin you likely will have race Conditions... you can write in the InputStream before to read or you can read from InputStream before write...
This is my code, my english skill is bad I hope all you can understand the problem and the solution to simulate write in stdin from JUnit test.
private void readFromConsole(String data) throws InterruptedException {
System.setIn(new ByteArrayInputStream(data.getBytes()));
Thread rC = new Thread() {
#Override
public void run() {
study = new Study();
study.read(System.in);
}
};
rC.start();
rC.join();
}
I've found it helpful to create an interface that defines methods similar to java.io.Console and then use that for reading or writing to the System.out. The real implementation will delegate to System.console() while your JUnit version can be a mock object with canned input and expected responses.
For example, you'd construct a MockConsole that contained the canned input from the user. The mock implementation would pop an input string off the list each time readLine was called. It would also gather all of the output written to a list of responses. At the end of the test, if all went well, then all of your input would have been read and you can assert on the output.
Related
I came up with a problem while trying to write a JUnit test for one specific method.
I searched for possible solutions but many of them were not helpful as the output was not dependent on the input. Any help would be much appreciated.
My class method looks like this:
public static void method1() {
Scanner input = new Scanner(System.in);
String state = input.nextLine();
if( /* condition dependent on state value */ ) {
System.out.println("...");
} else {
System.out.println("..."+state+"...");
}
}
How to write a JUnit test for it, can Robot class somehow solve the problem?
If you extract the logic to a separate function like
public static void method1() {
Scanner input = new Scanner(System.in);
String state = input.nextLine();
System.out.println(processingLogic(state));
}
static String processingLogic(String state) {
if ( /* condition dependent on state value */) {
return "some value";
} else {
return "some other value";
}
}
you can write a unit test for that function to see that it works correctly.
You can manipulate System.in and System.out using System.setIn() etc. For instance
System.setIn(new ByteArrayInputStream("test data".getBytes()));
However, I have the feeling that for your case, changing your method in a way that #p-j-meisch suggested in https://stackoverflow.com/a/59513668/2621917 is much better.
I'm new to programmming and I have this simple method:
public double input() {
double result = 0;
Scanner scanner = new Scanner(System.in);
if (scanner.hasNextDouble()) {
result = scanner.nextDouble();
} else {
System.out.print("Please, type numbers!\n");
}
return result;
}
The question is how to simulate (emulate) user's input from the keyboard in junit test.
Pass a Scanner as input parameter to the method you want to test.
In your test code, you can create a Scanner instance from a string:
Scanner scanner = new Scanner("the sample user input");
And then in the production code, you can pass new Scanner(System.in) to the method.
You should read more about dependency injection.
Your Class shouldn't be tightly coupled with other classes. Dependencies can be provided to objects at multiple levels according to the need.
Using constructor/setter if it is a field.
Using method parameters if the scope is just in a method.
In your case as soon as you say:-
Scanner scanner = new Scanner(System.in);
Now your code is fully coupled with System.in stream. Instead you should inject this as a parameter to your method in below format.
public double input(InputStream inputStream) {
double result = 0;
Scanner scanner = new Scanner(inputStream);
if (scanner.hasNextDouble()) {
result = scanner.nextDouble();
} else {
System.out.print("Please, type numbers!\n");
}
return result;
}
Now from your main code you can call it with System.in. From your test class you call it with any InputStream. Mostly we use a mock/stub for it.
Note:- Above it just an example, and can be change according to need.
I made a simple chatbot that responds to certain prompts with string output in Java. I want this program to output it's responses to an element on an HTML based webpage, and read input from the a different element on the same page.
Does anyone know how I could accomplish this?
Here's the code if you're interested:
import java.util.Scanner;
public class botRun
{
#SuppressWarnings("resource")
public static void main(String[] args)
{
PepperBot bot = new PepperBot();
Scanner in = new Scanner(System.in);
String input = in.nextLine();
while(true)
{
if(bot.shouldRespond(input))
{
System.out.println(bot.getRespond(input));
}
input = in.nextLine();
}
}
}
all other methods, "shouldRespond(String x)" and getRespond(String x) are in a separate class for object "PepperBot()" and check if the bot should respond and get the appropriate response respectively.
Pretty much any solution will do, as long as it isn't costly.
I am trying to write Junit test case for the function given below:
class A{
int i;
void set()
{
Scanner in=new Scanner(System.in);
i=in.nextInt();
}
}
Now my problem is when i create a Junit test case for it, it does not except input from user:
public void testSet() throws FileNotFoundException {
System.out.println("set");
A instance = new A();
int i=1;
instance.set(i);
// TODO review the generated test code and remove the default call to fail.
//fail("The test case is a prototype.");
}
Please suggets what should i do to accept input from user.
You can use System.setIn() to mock user input:
String inputData = "user input data";
System.setIn(new java.io.ByteArrayInputStream(inputData.getBytes()));
Now if you call your set() method it will read the data from your string rather than from standard input.
I have only one method main. How to check System.out.println() and replace Scanner to input values automatically using JUnit?
P.S. Please, provide some solutions...
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int[] arr = new int[4];
for (int i = 0; i < arr.length; i++) {
arr[i] = scanner.nextInt();
}
for (int i = 0; i < arr.length; i++) {
int res = 0;
int k = 0;
int num = arr[i];
/*.....*/
System.out.println(num);
}
}
Ideally, extract the awkward dependencies so that you can test without them. Change main to simply:
public static void main(String[] args) {
doWork(new Scanner(System.in), System.out);
}
// TODO: Rename to something meaningful
public static void doWork(Scanner input, PrintStream output) {
// Remainder of code
}
(Consider using a Writer instead of a PrintStream for output.)
Then you don't really need to unit test main - but you can test doWork using a Scanner based on a StringReader, and output based on a StringWriter, providing whatever input you want and checking the output.
I faced a similar issue and this is what I ended up doing.
First off, I'd suggest doing as #Jon-Skeet suggests and instead of using the main(String[]) method of the class, create a separate method.
Then you can have that method take in an InputStream as a parameter and then create a Scanner object within the method that uses the passed InputStream as its source. That way you can pass any InputStream, such as System.in, to the method when it's called (elaboration below).
package my.package;
import ...;
public class MyClass
{
public static void myMethod(InputStream inputStream)
{
Scanner inputScanner = new Scanner(inputStream);
// Do stuff with the Scanner such as...
String input = inputScanner.nextLine();
System.out.println("You inputted " + input);
}
}
Now, in your production source code you can call myMethod and pass it System.in as an argument as such, myMethod(System.in);
And then in your unit tests, you can create mock input values via a ByteArrayInputStream:
package my.package;
import ...;
public class MyClassTest
{
#Test
void testMyMethod()
{
// Simulates a user inputting the string "Mock input" and hitting enter
assertDoesNotThrow(myMethod(new ByteArrayInputStream("Mock input\n".getBytes())));
}
}
And voila, you now have a way to pass your method mock input as well as it being more modular overall.
I just want to point out without getting too much into it, that when working with System.in, one needs to be careful about closing it and in unit tests when working with input streams, one needs to be careful about reusing a reference to the same InputStream as its state can persist across uses.