Question

I am trying to use JUnitCore.runClasses() and I can get it running using the following code

JUnitCore.runClasses(testClass.class);

But i was curious, as runClasses() can take any number of parameters, is it possible to use code similar to the following?

Class c = testClass.class;
JUnitCore.runClasses(c);

Or

List<Class> c = new ArrayList<>{test1.class, test2.class, test3.class};
JUnitCore.runClasses(c);

I am asking this as if you try to pass a java.io.File type to JUnitCore.runClasses() you get the following error

no suitable method found for runClasses(java.io.File)
method org.junit.runner.JUnitCore.runClasses(java.lang.Class<?>...) is not applicable
  (argument type java.io.File does not conform to vararg element type java.lang.Class<?>)
method org.junit.runner.JUnitCore.runClasses(org.junit.runner.Computer,java.lang.Class<?>...) is not applicable
  (actual argument java.io.File cannot be converted to org.junit.runner.Computer by method invocation conversion)

Answer 1

I assume you are trying to do the following:

You have a file containing a java class which you want to run using JUnitCore.

To acomplish this you will have to:

1. Load the class, this can be done by using a custom class loader. A better approach would be to just include the class into your application
2. Now you can invoke JUnitCore.runClasses(loadedClass);

Code sample:

File file = new File("path to your file");
File dir = file.getParentFile();
URL url = new URL("file://" + dir.getAbsolutePath());
URLClassLoader classLoader = new URLClassLoader(new URL[]{url});
Class<?> clazz = classLoader.findClass("ClassName");
JUnitCore.runClasses(clazz);

The example will only work if the class does not have a package. You can write an own class loader to control the class loading process. See the javadoc for URLClassLoader to learn how this class loader works. For writing a custom class loader you could consult this.