test: improve PatcherTest

src/main/kotlin/net/revanced/patcher/writer/ASMWriter.kt

@@ -7,4 +7,14 @@ object ASMWriter {
     fun InsnList.setAt(index: Int, node: AbstractInsnNode) {
         this[this.get(index)] = node
     }
+    fun InsnList.insertAt(index: Int, vararg nodes: AbstractInsnNode) {
+        this.insert(this.get(index), nodes.toInsnList())
+    }
+
+    // TODO(Sculas): Should this be public?
+    private fun Array<out AbstractInsnNode>.toInsnList(): InsnList {
+        val list = InsnList()
+        this.forEach { list.add(it) }
+        return list
+    }
 }

src/test/kotlin/net/revanced/patcher/PatcherTest.kt

@@ -4,10 +4,13 @@ import net.revanced.patcher.patch.Patch
 import net.revanced.patcher.patch.PatchResultSuccess
 import net.revanced.patcher.signature.Signature
 import net.revanced.patcher.util.ExtraTypes
+import net.revanced.patcher.util.TestUtil
+import net.revanced.patcher.writer.ASMWriter.insertAt
 import net.revanced.patcher.writer.ASMWriter.setAt
 import org.objectweb.asm.Opcodes.*
 import org.objectweb.asm.Type
 import org.objectweb.asm.tree.*
+import java.io.PrintStream
 import kotlin.test.Test
 
 internal class PatcherTest {
@@ -46,20 +49,51 @@ internal class PatcherTest {
                 val mainMethod = patcher.cache.methods["mainMethod"]
                 // Get the instruction list
                 val instructions = mainMethod.method.instructions!!
-                // Let's modify it, so it prints "Hello, ReVanced!"
-                // Get the start index of our opcode pattern
-                // This will be the index of the LDC instruction
+
+                // Let's modify it, so it prints "Hello, ReVanced! Editing bytecode."
+                // Get the start index of our opcode pattern.
+                // This will be the index of the LDC instruction.
                 val startIndex = mainMethod.scanData.startIndex
-                // Create a new Ldc node and replace the LDC instruction
-                val stringNode = LdcInsnNode("Hello, ReVanced!");
+                TestUtil.assertNodeEqual(LdcInsnNode("Hello, world!"), instructions[startIndex]!!)
+                // Create a new LDC node and replace the LDC instruction.
+                val stringNode = LdcInsnNode("Hello, ReVanced! Editing bytecode.")
                 instructions.setAt(startIndex, stringNode)
-                // Now lets print our string to the console output
-                // First create a list of instructions
-                val printCode = InsnList();
-                printCode.add(LdcInsnNode("Hello, ReVanced!"))
-                printCode.add(MethodInsnNode(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V"))
-                // Add the list after the second instruction by our pattern
-                instructions.insert(instructions[startIndex + 1], printCode)
+
+                // Now lets print our string twice!
+                // Insert our instructions after the second instruction by our pattern.
+                // This will place our instructions after the original INVOKEVIRTUAL call.
+                // You could also copy the instructions from the list and then modify the LDC instruction again,
+                // but this is to show a more advanced example of writing bytecode using the patcher and ASM.
+                instructions.insertAt(
+                    startIndex + 1,
+                    FieldInsnNode(
+                        GETSTATIC,
+                        Type.getInternalName(System::class.java), // "java/io/System"
+                        "out",
+                        Type.getInternalName(PrintStream::class.java) // "java.io.PrintStream"
+                    ),
+                    LdcInsnNode("Hello, ReVanced! Adding bytecode."),
+                    MethodInsnNode(
+                        INVOKEVIRTUAL,
+                        Type.getInternalName(PrintStream::class.java), // "java/io/PrintStream"
+                        "println",
+                        Type.getMethodDescriptor(
+                            Type.VOID_TYPE,
+                            Type.getType(String::class.java)
+                        ) // "(Ljava/lang/String;)V"
+                    )
+                )
+
+                // Our code now looks like this:
+                // public static main(java.lang.String[] arg0) { // Method signature: ([Ljava/lang/String;)V
+                //     getstatic java/lang/System.out:java.io.PrintStream
+                //     ldc "Hello, ReVanced! Editing bytecode." (java.lang.String) // We overwrote this instruction.
+                //     invokevirtual java/io/PrintStream.println(Ljava/lang/String;)V
+                //     getstatic java/lang/System.out:java.io.PrintStream // This instruction and the 2 instructions below are written manually.
+                //     ldc "Hello, ReVanced! Adding bytecode." (java.lang.String)
+                //     invokevirtual java/io/PrintStream.println(Ljava/lang/String;)V
+                //     return
+                // }
 
                 // Finally, tell the patcher that this patch was a success.
                 // You can also return PatchResultError with a message.

src/test/kotlin/net/revanced/patcher/util/TestUtil.kt

@@ -1,14 +1,44 @@
 package net.revanced.patcher.util
 
 import org.objectweb.asm.tree.AbstractInsnNode
-import kotlin.test.assertTrue
+import org.objectweb.asm.tree.FieldInsnNode
+import org.objectweb.asm.tree.LdcInsnNode
+import kotlin.test.fail
 
 object TestUtil {
-    fun <T: AbstractInsnNode> assertNodeEqual(a: T, b: T) {
-
+    fun <T: AbstractInsnNode> assertNodeEqual(expected: T, actual: T) {
+        val a = expected.nodeString()
+        val b = actual.nodeString()
+        if (a != b) {
+            fail("expected: $a,\nactual: $b\n")
+        }
     }
 
     private fun AbstractInsnNode.nodeString(): String {
-
+        val sb = NodeStringBuilder()
+        when (this) {
+            // TODO: Add more types
+            is LdcInsnNode -> sb
+                .addType("cst", cst)
+            is FieldInsnNode -> sb
+                .addType("owner", owner)
+                .addType("name", name)
+                .addType("desc", desc)
+        }
+        return "(${this::class.simpleName}): (type = $type, opcode = $opcode, $sb)"
     }
-}
+}
+
+private class NodeStringBuilder {
+    private val sb = StringBuilder()
+
+    fun addType(name: String, value: Any): NodeStringBuilder {
+        sb.append("$name = \"$value\", ")
+        return this
+    }
+
+    override fun toString(): String {
+        val s = sb.toString()
+        return s.substring(0 until s.length - 2) // remove the last ", "
+    }
+}