解决了，原因是创建项目语言选择错误，选了 kotlin，后来重新创建一个java的就成功了。另外还有adb.exe打开失败问题，下载了adb的最新安装包把文件替换了就解决了

01/30 18:29:55: Launching 'DemoTest()' on Android711.

Running tests

Starting Gradle Daemon...

Gradle Daemon started in 2 s 897 ms

> Configure project :app

WARNING:The option setting 'android.experimental.testOptions.emulatorSnapshots.maxSnapshotsForTestFailures=0' is experimental.

> Task :app:preBuild UP-TO-DATE

> Task :app:preDebugBuild UP-TO-DATE

> Task :app:compileDebugAidl NO-SOURCE

> Task :app:compileDebugRenderscript NO-SOURCE

> Task :app:generateDebugBuildConfig UP-TO-DATE

> Task :app:checkDebugAarMetadata UP-TO-DATE

> Task :app:generateDebugResValues UP-TO-DATE

> Task :app:generateDebugResources UP-TO-DATE

> Task :app:mergeDebugResources UP-TO-DATE

> Task :app:packageDebugResources UP-TO-DATE

> Task :app:parseDebugLocalResources UP-TO-DATE

> Task :app:createDebugCompatibleScreenManifests UP-TO-DATE

> Task :app:extractDeepLinksDebug UP-TO-DATE

> Task :app:processDebugMainManifest UP-TO-DATE

> Task :app:processDebugManifest UP-TO-DATE

> Task :app:processDebugManifestForPackage UP-TO-DATE

> Task :app:processDebugResources UP-TO-DATE

> Task :app:compileDebugKotlin UP-TO-DATE

> Task :app:javaPreCompileDebug UP-TO-DATE

> Task :app:compileDebugJavaWithJavac UP-TO-DATE

> Task :app:bundleDebugClasses UP-TO-DATE

> Task :app:preDebugAndroidTestBuild SKIPPED

> Task :app:compileDebugAndroidTestAidl NO-SOURCE

> Task :app:processDebugAndroidTestManifest UP-TO-DATE

> Task :app:generateDebugAndroidTestBuildConfig UP-TO-DATE

> Task :app:checkDebugAndroidTestAarMetadata UP-TO-DATE

> Task :app:compileDebugAndroidTestRenderscript NO-SOURCE

> Task :app:generateDebugAndroidTestResValues UP-TO-DATE

> Task :app:generateDebugAndroidTestResources UP-TO-DATE

> Task :app:mergeDebugAndroidTestResources UP-TO-DATE

> Task :app:processDebugAndroidTestResources UP-TO-DATE

> Task :app:compileDebugAndroidTestKotlin UP-TO-DATE

> Task :app:javaPreCompileDebugAndroidTest UP-TO-DATE

> Task :app:compileDebugAndroidTestJavaWithJavac

D:\Android\ASWorkspace\MKApplication\app\src\androidTest\java\com\mk\MKTest.java:5: 错误: 程序包android.support.test.uiautomator不存在

import android.support.test.uiautomator.UiDevice;

                                       ^

D:\Android\ASWorkspace\MKApplication\app\src\androidTest\java\com\mk\MKTest.java:16: 错误: 找不到符号

    public UiDevice mUidevice;

           ^

  符号:   类 UiDevice

  位置: 类 MKTest

D:\Android\ASWorkspace\MKApplication\app\src\androidTest\java\com\mk\MKTest.java:13: 错误: 找不到符号

@RunWith(AndriodJUnit4.class)

         ^

  符号: 类 AndriodJUnit4

D:\Android\ASWorkspace\MKApplication\app\src\androidTest\java\com\mk\MKTest.java:21: 错误: 找不到符号

        mUidevice= UiDevice.getInstance(mInstrumentation);

                   ^

  符号:   变量 UiDevice

  位置: 类 MKTest

4 个错误

> Task :app:compileDebugAndroidTestJavaWithJavac FAILED

25 actionable tasks: 1 executed, 24 up-to-date

FAILURE: Build failed with an exception.

* What went wrong:

Execution failed for task ':app:compileDebugAndroidTestJavaWithJavac'.

> Compilation failed; see the compiler error output for details.

* Try:

Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 16s