Provide alternate diffing mechanism

src/main/kotlin/com/netflix/java/refactor/JavaSource.kt

@@ -4,6 +4,8 @@ import com.netflix.java.refactor.find.*
 import com.sun.tools.javac.code.Symbol
 import com.sun.tools.javac.tree.JCTree
 import java.nio.file.Files
+import java.util.function.Consumer
+import kotlin.concurrent.thread
 
 class JavaSource(internal val cu: CompilationUnit) {
     var changedFile = false
@@ -51,4 +53,6 @@ class JavaSource(internal val cu: CompilationUnit) {
         val after = text()
         return InMemoryDiffEntry(file().toString(), before, after).diff
     }
+
+    fun beginDiff() = JavaSourceDiff(this)
 }

src/main/kotlin/com/netflix/java/refactor/JavaSourceDiff.kt

@@ -0,0 +1,10 @@
+package com.netflix.java.refactor
+
+class JavaSourceDiff(private val source: JavaSource) {
+    val before = source.text()
+
+    fun gitStylePatch(): String {
+        val after = source.text()
+        return InMemoryDiffEntry(source.file().toString(), before, after).diff
+    }
+}

src/test/kotlin/com/netflix/java/refactor/JavaSourceTest.kt

@@ -87,11 +87,13 @@ class JavaSourceTest : AbstractRefactorTest() {
         """)
 
         val source = parseJava(a, b, c)
-        val diff = source.diff {
+        val diff1 = source.beginDiff()
+
+        val diff2 = source.diff {
             refactor().changeType("B", "C").fix()
         }
-        
-        assertEquals("""
+
+        val expectedDiff = """
             |diff --git a/${a.absolutePath} b/${a.absolutePath}
             |index 70f03ee..b82f543 100644
             |--- a/${a.absolutePath}
@@ -105,6 +107,9 @@ class JavaSourceTest : AbstractRefactorTest() {
             |    }
             | }
             |
-        """.trimMargin(), diff)
+        """.trimMargin()
+
+        assertEquals(expectedDiff, diff1.gitStylePatch())
+        assertEquals(expectedDiff, diff2)
     }
 }