diff --git a/platform/diff-impl/diff-tests.iml b/platform/diff-impl/diff-tests.iml
index b85fb62c1d37..64aa21cbf410 100644
--- a/platform/diff-impl/diff-tests.iml
+++ b/platform/diff-impl/diff-tests.iml
@@ -14,5 +14,6 @@
     <orderEntry type="module" module-name="platform-impl" />
     <orderEntry type="module" module-name="vcs-api-core" />
     <orderEntry type="module" module-name="diff-impl" scope="TEST" />
+    <orderEntry type="library" scope="TEST" name="mockito" level="project" />
   </component>
 </module>
\ No newline at end of file
diff --git a/platform/diff-impl/tests/com/intellij/diff/tools/util/PrevNextIterableTest.kt b/platform/diff-impl/tests/com/intellij/diff/tools/util/PrevNextIterableTest.kt
new file mode 100644
index 000000000000..3969ec41b822
--- /dev/null
+++ b/platform/diff-impl/tests/com/intellij/diff/tools/util/PrevNextIterableTest.kt
@@ -0,0 +1,186 @@
+/*
+ * Copyright 2000-2015 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.intellij.diff.tools.util
+
+import com.intellij.diff.DiffTestCase
+import com.intellij.openapi.editor.CaretModel
+import com.intellij.openapi.editor.LogicalPosition
+import com.intellij.openapi.editor.ex.DocumentEx
+import com.intellij.openapi.editor.ex.EditorEx
+import org.mockito.Mockito
+import kotlin.test.assertEquals
+
+class PrevNextIterableTest : DiffTestCase() {
+  fun testIterable() {
+    test(1) {
+      check(!0 - 0, null, null)
+    }
+
+    test(10) {
+      check(!0 - 9, null, null)
+    }
+
+    test(10, !5 - 6) {
+      check(!0 - 4, null, 0)
+      check(!5 - 6, null, null)
+      check(!7 - 9, 0, null)
+    }
+
+    test(10, !5) {
+      check(!0 - 4, null, 0)
+      check(!5 - 5, null, null)
+      check(!6 - 9, 0, null)
+    }
+
+    test(10, !3 - 4, !6 - 7) {
+      check(!0 - 2, null, 0)
+      check(!3 - 4, null, 1)
+      check(!5 - 5, 0, 1)
+      check(!6 - 7, 0, null)
+      check(!8 - 9, 1, null)
+    }
+
+    test(25, !1 - 3, !6 - 7, !9 - 12, !15 - 20) {
+      check(!0 - 0, null, 0)
+      check(!1 - 3, null, 1)
+      check(!4 - 5, 0, 1)
+      check(!6 - 7, 0, 2)
+      check(!8 - 8, 1, 2)
+      check(!9 - 12, 1, 3)
+      check(!13 - 14, 2, 3)
+      check(!15 - 20, 2, null)
+      check(!21 - 24, 3, null)
+    }
+
+    test(11, !10) {
+      check(!0 - 9, null, 0)
+      check(!10, null, null)
+    }
+
+    test(10, !10) {
+      check(!0 - 8, null, 0)
+      check(!9, null, null)
+    }
+
+    test(10, !0) {
+      check(!0, null, null)
+      check(!1 - 9, 0, null)
+    }
+
+    test(10, !3 - 4, !5 - 6) {
+      check(!0 - 2, null, 0)
+      check(!3 - 4, null, 1)
+      check(!5 - 6, 0, null)
+      check(!7 - 9, 1, null)
+    }
+
+    test(10, !3 - 4, !5, !5 - 6) {
+      check(!0 - 2, null, 0)
+      check(!3 - 4, null, 1)
+      check(!5 - 5, 0, null)
+      check(!6 - 6, 1, null)
+      check(!7 - 9, 2, null)
+    }
+
+    test(10, !3, !5, !6, !7) {
+      check(!0 - 2, null, 0)
+      check(!3 - 3, null, 1)
+      check(!4 - 4, 0, 1)
+      check(!5 - 5, 0, 2)
+      check(!6 - 6, 1, 3)
+      check(!7 - 7, 2, null)
+      check(!8 - 9, 3, null)
+    }
+  }
+
+  private fun test(total: Int, vararg changes: Range, handler: MyIterable.() -> Unit) {
+    val testHelper = MyIterable(changes.asList(), total)
+    testHelper.handler()
+
+    // first and last line
+    testHelper.checkPrev(0, null)
+    testHelper.checkNext(total - 1, null)
+    testHelper.checkNext(total, null)
+  }
+}
+
+private class MyIterable(private val ranges: List<Range>, private val total: Int) : PrevNextDifferenceIterableBase<Range>() {
+  private var current: Int = 0
+  private var lastTarget: Int? = null
+
+  override fun getChanges(): List<Range> = ranges
+  override fun getStartLine(change: Range): Int = change.start
+  override fun getEndLine(change: Range): Int = change.end
+  override fun scrollToChange(change: Range) {
+    lastTarget = ranges.indexOf(change)
+  }
+
+  override fun getEditor(): EditorEx {
+    val document = Mockito.mock(DocumentEx::class.java)
+    val editorEx = Mockito.mock(EditorEx::class.java)
+    val caretModel = Mockito.mock(CaretModel::class.java)
+    Mockito.`when`(document.lineCount).thenReturn(total)
+    Mockito.`when`(editorEx.document).thenReturn(document)
+    Mockito.`when`(editorEx.caretModel).thenReturn(caretModel)
+    Mockito.`when`(caretModel.logicalPosition).thenReturn(LogicalPosition(current, 0))
+    return editorEx
+  }
+
+
+  fun check(range: Range, prev: Int?, next: Int?) {
+    for (current in range.start..range.end - 1) {
+      check(current, prev, next)
+    }
+  }
+
+  fun check(current: Int, prev: Int?, next: Int?) {
+    checkPrev(current, prev)
+    checkNext(current, next)
+  }
+
+  fun checkPrev(current: Int, prev: Int?) {
+    this.current = current
+
+    if (prev == null) {
+      assert(!canGoPrev())
+    }
+    else {
+      assert(canGoPrev())
+      lastTarget = null
+      goPrev()
+      assertEquals(prev, lastTarget)
+    }
+  }
+
+  fun checkNext(current: Int, next: Int?) {
+    this.current = current
+
+    if (next == null) {
+      assert(!canGoNext())
+    }
+    else {
+      assert(canGoNext())
+      lastTarget = null
+      goNext()
+      assertEquals(next, lastTarget)
+    }
+  }
+}
+
+private data class Range(val start: Int, var end: Int = start)
+
+private operator fun Int.not(): Range = Range(this)
+private operator fun Range.minus(col: Int): Range = Range(this.start, col + 1)