How to prevent logging noise during startup in @SpringBootTest?

Edited

Create logback-test.xml in your test resource (\test\resources), Then put bellow snippet into it

<configuration>
    <include resource="org/springframework/boot/logging/logback/base.xml" />
    <logger name="org.springframework" level="OFF"/>
</configuration>

It prints default system INFOs, not startup noise logs. (As you wanted)

And dependency of test can be as follows

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
</dependency>

You will need to create one logback-test.xml in your \test\resources directory, contents of this file can be following

<?xml version="1.0" encoding="UTF-8"?>
<configuration />

Why empty ?

Because you'd not want anything to be logged at this point in time, hence - empty configuration.

If you wish to find out more specific you can see some examples here

First of all: I know, this is not a real answer, but way too long for a comment.

Using the log4j dependency didn't changed much in my output.

My POM

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-log4j2</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

My application.properties is empty, so no log config there.

My test

package com.example.demo;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT, properties = "logging.level.root=")
public class DemoApplicationTests
{

    @Test
    public void test()
    {
        System.out.println("Katzenbilder sind doof");
    }

}

Running the tests from within IntelliJ with logging.level.root=OFF leads to this output

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.0.4.RELEASE)

##### Optional[Hallo Welt]
##### Hallo Welt
Katzenbilder sind doof

Process finished with exit code 0

The two lines with #####are System.out.println() from a test bean.

Running the test with logging.level.root=INFO I get the expected clutter of Spring log messages.

I also, just for the sake of validation, put logging.level.root=INFO in my application.properties and had it to OFF in the test. No clutter, just the System.out.println() messages.