How to mock a Files static method with Mockito

user_834045 0
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I have a method in my utilities:

public void createDirectories(final Path root, final Scaffolding scaffolding) throws FileAlreadyExistsException {
    if (Files.exists(root)) {
        throw new FileAlreadyExistsException("Root directory " + root.toString() + " already exists.");
    } else {
        Files.createDirectories(root);
        // Create directories from the scaffolding object
    }
}

I want to mock Files so I can test to make sure Files.createDirectories with the expected fields are called or not.

Can I do this with Mockito? Or do I need to actually create the directories and check for their existence in some tmp folder?

mockito junit java
3 Answers

I'm sending you an example, which allows you to use the FileSystems Mock in a transparent way

@Test
    @ExtendWith(MockfsExtension.class)
    void testExecute_MockFSNew(FileSystem fileSystem) throws Exception {
        
        Path master = Files.createDirectories(Paths.get("/fakedir/conf/java/rest/master"));
        Path homologacao = Files.createDirectories(fileSystem.getPath("/fakedir/conf/java/rest/homologacao"));
        Path dev = Files.createDirectories(fileSystem.getPath("/fakedir/conf/java/rest/dev"));

    }

Paths.get return a mock fs, this is done using Mockito.mockStatic

It's also injecting FileSystem in paramter

using

package br.com.pulse.starter.builder.steps.impl;

import java.nio.file.FileSystem;
import java.nio.file.FileSystems;

import org.junit.jupiter.api.extension.AfterEachCallback;
import org.junit.jupiter.api.extension.BeforeEachCallback;
import org.junit.jupiter.api.extension.ExtensionContext;
import org.junit.jupiter.api.extension.ParameterContext;
import org.junit.jupiter.api.extension.ParameterResolutionException;
import org.junit.jupiter.api.extension.ParameterResolver;
import org.mockito.MockedStatic;
import org.mockito.Mockito;

import com.github.marschall.memoryfilesystem.MemoryFileSystemBuilder;

public class MockfsExtension implements BeforeEachCallback, AfterEachCallback , ParameterResolver  {

    MockedStatic<FileSystems> mock;

    private FileSystem fileSystem;

    public FileSystem getFileSystem() {
        return this.fileSystem;
    }


    @Override
    public void beforeEach( ExtensionContext context ) throws Exception {
        this.fileSystem = MemoryFileSystemBuilder.newEmpty().build();
        mock = Mockito.mockStatic(FileSystems.class);

        mock.when(() -> FileSystems.getDefault()).then(invocation -> {
            System.out.println("Requested FakeFs >>>");
            return fileSystem;
        });

    }
    

    @Override
    public void afterEach( ExtensionContext context ) throws Exception {

        if (this.fileSystem != null) {
            this.fileSystem.close();
        }

        mock.close();
    }

    @Override
    public boolean supportsParameter( ParameterContext parameterContext , ExtensionContext extensionContext ) throws ParameterResolutionException {
        return true;
    }

    @Override
    public Object resolveParameter( ParameterContext parameterContext , ExtensionContext extensionContext ) throws ParameterResolutionException {
        return this.fileSystem;
    }

}

See: https://github.com/marschall/memoryfilesystem https://github.com/marschall/memoryfilesystem/issues/130

user_9558570
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