git: add test for commit via staging area

plugins/git4idea/tests/git4idea/tests/GitCommitTest.kt

@@ -35,7 +35,7 @@ import java.io.File
 import java.util.*
 
 
-class GitCommitTest : GitSingleRepoTest() {
+open class GitCommitTest : GitSingleRepoTest() {
   private val myMovementProvider = MyExplicitMovementProvider()
 
   override fun getDebugLogCategories() = super.getDebugLogCategories().plus("#" + GitCheckinEnvironment::class.java.name)
@@ -533,7 +533,7 @@ class GitCommitTest : GitSingleRepoTest() {
 
   fun `test commit rename with conflicting staged rename`() {
     `assume version where git reset returns 0 exit code on success `()
-    assumeTrue(Registry.`is`("git.force.commit.using.staging.area"))
+    assumeTrue(Registry.`is`("git.force.commit.using.staging.area")) // known bug in "--only" implementation
 
     tac("a.txt", "file content")
 

plugins/git4idea/tests/git4idea/tests/GitStagingCommitTest.kt

@@ -0,0 +1,20 @@
+// Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package git4idea.tests
+
+import com.intellij.openapi.util.registry.Registry
+
+class GitStagingCommitTest : GitCommitTest() {
+  override fun setUp() {
+    super.setUp()
+    Registry.get("git.force.commit.using.staging.area").setValue(true)
+  }
+
+  override fun tearDown() {
+    try {
+      Registry.get("git.force.commit.using.staging.area").resetToDefault()
+    }
+    finally {
+      super.tearDown()
+    }
+  }
+}