testing scripts: report error if run configuration uses a fork mode

platform/build-scripts/groovy/org/jetbrains/intellij/build/impl/JUnitRunConfigurationProperties.groovy

@@ -59,6 +59,11 @@ class JUnitRunConfigurationProperties {
       testClassPatterns = []
     }
 
+    String forkMode = first(configuration.fork_mode)?.@value
+    if (forkMode != null && forkMode != "none") {
+      messages.error("Cannot run $file.name configuration: fork mode '$forkMode' is not supported")
+    }
+
     List<String> requiredArtifacts =
       first(configuration.method)?.option?.
             find { it.@name == "BuildArtifacts" && it.@enabled == "true" }?.

platform/build-scripts/tests/testResources/org/jetbrains/intellij/build/runConfigurations/test_method_fork_mode.xml

@@ -0,0 +1,16 @@
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="test class fork" type="JUnit" factoryName="JUnit">
+    <module name="main-module"/>
+    <option name="ALTERNATIVE_JRE_PATH_ENABLED" value="false"/>
+    <option name="MAIN_CLASS_NAME" value="com.example.test.MainTest"/>
+    <option name="TEST_OBJECT" value="class"/>
+    <option name="VM_PARAMETERS" value="-ea -Xmx512m"/>
+    <option name="PARAMETERS" value=""/>
+    <option name="WORKING_DIRECTORY" value="file://$PROJECT_DIR$/bin"/>
+    <option name="PASS_PARENT_ENVS" value="true"/>
+    <option name="TEST_SEARCH_SCOPE">
+      <value defaultName="moduleWithDependencies"/>
+    </option>
+    <fork_mode value="method"/>
+  </configuration>
+</component>

platform/build-scripts/tests/testSrc/org/jetbrains/intellij/build/JUnitRunConfigurationPropertiesTest.kt

@@ -4,6 +4,7 @@
 package org.jetbrains.intellij.build
 
 import com.intellij.util.io.URLUtil
+import junit.framework.AssertionFailedError
 import org.jetbrains.intellij.build.impl.JUnitRunConfigurationProperties
 import org.junit.Assert.assertEquals
 import org.junit.Test
@@ -40,6 +41,11 @@ class JUnitRunConfigurationPropertiesTest {
     assertEquals(emptyList<String>(), properties.requiredArtifacts)
   }
 
+  @Test(expected = AssertionFailedError::class)
+  fun `load test with method fork mode`() {
+    loadRunConfiguration("test_method_fork_mode.xml")
+  }
+
   private fun loadRunConfiguration(fileName: String): JUnitRunConfigurationProperties {
     val url = JUnitRunConfigurationPropertiesTest::class.java.getResource("runConfigurations/$fileName")
     return JUnitRunConfigurationProperties.loadRunConfiguration(URLUtil.urlToFile(url), MockBuildMessages())