报错信息：

Error:Execution failed for task ':app:preDebugAndroidTestBuild'.

> Conflict with dependency 'com.android.support:support-annotations' in project ':app'. Resolved versions for app (26.1.0) and test app (27.1.1) differ. See [https://d.android.com/r/tools/test-apk-dependency-conflicts.html](https://d.android.com/r/tools/test-apk-dependency-conflicts.html) for details. Information:Gradle tasks [:app:generateDebugSources, :app:generateDebugAndroidTestSources, :app:mockableAndroidJar]

报错内容提示版本冲突：
应用程序版本和测试应用程序版本不一致冲突:

解决方案
参见stackoverflow：

1.在dependencies中添加代码
compile 'com.android.support:support-annotations:27.1.1'

例如：

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:support-annotations:27.1.1'    
    implementation 'com.android.support.constraint:constraint-layout:1.1.0'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}

1. 按照官方文档操作:
   官方文档案例
   我的项目中是这么用的
   在顶层gradle文件中加入ext代码块

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.1'
        

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

// This block encapsulates custom properties and makes them available to all
// modules in the project.
ext {
    // The following are only a few examples of the types of properties you can define.
    compileSdkVersion = 26
    buildToolsVersion = "27.0.3"

    // You can also use this to specify versions for dependencies. Having consistent
    // versions between modules can avoid behavior conflicts.
    supportLibVersion = "27.1.1"
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

然后在模块级中的gradle文件中使用 也就是app/build.gradle

apply plugin: 'com.android.application'

android {

    compileSdkVersion rootProject.ext.compileSdkVersion
    buildToolsVersion rootProject.ext.buildToolsVersion

    defaultConfig {
        applicationId "com.chinalife.mcp.chinalife"
        minSdkVersion 15
        targetSdkVersion 26
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:27.1.1'
    implementation 'com.android.support.constraint:constraint-layout:1.1.0'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}