如果您不打算实施测试代码，请从您的应用中删除junit。

  apply plugin：'com.android.application'

 android {
 compileSdkVersion 26 
 defaultConfig {
 applicationIdcom.example.elili.deltacalculator
 minSdkVersion 18 
 targetSdkVersion 26 
 versionCode 1 
 versionName1.0
} 
 buildTypes {
 release {
 minifyEnabled false 
 proguardFiles getDefaultProguardFile（'proguard-android.txt'），'proguard-rules.pro' 




依赖关系{
 implementation fileTree（dir：'libs'，include：['* .jar']）
实现'com.android.support:appcompat-v7:26.1.0'
 implementation'com.android.support.constraint：constraint-layout：1.1.0'
 

I created a new project as usual andafter the gradle running I get this error: `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 for details.`

This is my fresh project gradle:

apply plugin: 'com.android.application'

android {
compileSdkVersion 26
defaultConfig {
    applicationId "com.example.elili.deltacalculator"
    minSdkVersion 18
    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-v7:26.1.0'
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'

I have zero ideas on how to fix it...

If you are not going to implement testing code, then remove junit from your app. You can replace your gradle by below.

apply plugin: 'com.android.application'

android {
compileSdkVersion 26
defaultConfig {
    applicationId "com.example.elili.deltacalculator"
    minSdkVersion 18
    targetSdkVersion 26
    versionCode 1
    versionName "1.0"
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}


dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support:appcompat-v7:26.1.0'
implementation 'com.android.support.constraint:constraint-layout:1.1.0'