Add test snapshot utility

Build.java

@@ -63,7 +63,7 @@ public class Build {
 
       case "test":
         buildJtags(mainClass, sourcePaths, classPaths);
-        runTests();
+        runTests(arguments.toArray(String[]::new));
         break;
 
       default:
@@ -96,7 +96,7 @@ public class Build {
         ".");
   }
 
-  static void runTests() {
+  static void runTests(String[] args) {
     String mainClass = "TestJtags";
     String[] sourcePaths = glob("src/test/java/**.java");
 
@@ -107,6 +107,6 @@ public class Build {
       }
     }
 
-    System.exit(runJava(new String[0], new String[] {"-enableassertions"}, mainClass));
+    System.exit(runJava(new String[0], new String[] {"-enableassertions"}, mainClass, args));
   }
 }

nobuild/NoBuild.java

@@ -33,7 +33,6 @@ import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
-import java.lang.ProcessBuilder.Redirect;
 import java.net.URI;
 import java.net.URL;
 import java.nio.file.FileSystems;

src/test/java/TestJtags.java

@@ -1,9 +1,6 @@
 import static notest.Test.Util.*;
 
-import java.io.BufferedReader;
-import java.io.FileReader;
 import java.io.IOException;
-import java.nio.file.Path;
 import notest.Test;
 
 class TestJtags {
@@ -17,19 +14,14 @@ class TestJtags {
   static void basicExample() throws IOException {
     var process =
         runJava(
-                new String[] {"-Dlogger.level=CONFIG"},
-                Jtags,
-                "-o",
-                "-",
-                "src/test/java/examples/BasicExample.java");
+            new String[] {"-Dlogger.level=CONFIG"},
+            Jtags,
+            "-o",
+            "-",
+            "src/test/java/examples/BasicExample.java");
 
     var tags = readAllLines(process.inputReader());
 
-    Diff.diff(
-            tags,
-            readAllLines(new BufferedReader(new FileReader(
-                Path.of("src", "test", "java", "snapshots", "BasicExample.basicExample.1")
-                    .toFile()))))
-        .assertEqual();
+    getSnapshot().assertEquals(tags);
   }
 }

src/test/java/notest/Test.java

@@ -39,10 +39,13 @@ import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.PathMatcher;
 import java.nio.file.Paths;
+import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.HashMap;
 import java.util.IntSummaryStatistics;
 import java.util.List;
+import java.util.Map;
 import java.util.Optional;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -57,9 +60,27 @@ public @interface Test {
     public static Path javaHome = Paths.get(System.getProperty("java.home"));
     public static String javaClassPath = System.getProperty("java.class.path");
     public static String javaBin = javaHome.resolve("bin", "java").toString();
+    public static Path snapshotsPath = Path.of("src", "test", "java", "snapshots");
+
+    private static class Options {
+      boolean updateSnapshots = false;
+    }
+
+    private static Options options = new Options();
 
     /** Runs all tests in {@code testClass} */
     public static void runTests(Class<?> testClass, String[] args) {
+      var arguments = new ArrayDeque<String>(Arrays.asList(args));
+
+      switch (arguments.poll()) {
+        case "-u", "-update-snapshots":
+          options.updateSnapshots = true;
+          break;
+        case null:
+        default:
+          break;
+      }
+
       System.exit(doRunTests(testClass) ? 0 : 1);
     }
 
@@ -173,6 +194,11 @@ public @interface Test {
 
       /** Creates a {@code Diff} representing changes from {@code a} to {@code b} */
       public static Diff diff(List<String> a, List<String> b) {
+        if (a.equals(b)) return new Diff(List.of());
+
+        if (a.isEmpty()) a = List.of("");
+        if (b.isEmpty()) b = List.of("");
+
         int diffSize = 0;
         // longest common subsequence algorithm
         int[][] dp = new int[a.size() + 1][b.size() + 1];
@@ -251,6 +277,31 @@ public @interface Test {
       return lines;
     }
 
+    public static record Snapshot(Path path) {
+      public void assertEquals(List<String> result) throws IOException {
+        var lines = Files.readAllLines(path);
+        if (options.updateSnapshots && !lines.equals(result)) {
+          Files.write(path, result);
+          return;
+        }
+        Diff.diff(lines, result).assertEqual();
+      }
+    }
+
+    private static Map<String, Integer> snapshotCount = new HashMap<>();
+
+    public static Snapshot getSnapshot() throws IOException {
+      var stackFrame = new Throwable().getStackTrace()[1];
+      var className = stackFrame.getClassName();
+      var methodName = stackFrame.getMethodName();
+      var prefix = className + "." + methodName;
+      var snapshotNumber = snapshotCount.compute(prefix, (k, v) -> v == null ? 1 : ++v);
+      Path path = snapshotsPath.resolve(prefix + "." + snapshotNumber);
+      if (!snapshotsPath.toFile().exists()) snapshotsPath.toFile().mkdirs();
+      if (!path.toFile().exists()) Files.write(path, List.of());
+      return new Snapshot(path);
+    }
+
     /**
      * Pads string to center.
      *

src/test/java/snapshots/TestJtags.basicExample.1

@@ -1,9 +1,9 @@
 ABC
 !_TAG_FILE_ENCODING	utf-8
 !_TAG_FILE_SORTED	2	/0=unsorted, 1=sorted, 2=foldcase/
-BasicExample	src/test/java/examples/BasicExample.java	/^public class BasicExample {$/;"	Cls	package:examples
 InnerClass	src/test/java/examples/BasicExample.java	/^    class InnerClass {$/;"	Cls	package:examples	class:BasicExample
 method1	src/test/java/examples/BasicExample.java	/^  private boolean method1() {$/;"	mthd	class:BasicExample
-ABC		lorem ipsum dolor
-method2	src/test/java/examples/BasicExample.java	/^  public static void method2($/;"	mthd	file:	class:BasicExample
+method2	src/test/java/examples/BasicExample.java	/^          void method2() {}$/;"	mthd	class:(Anonymous)
+methodX	src/test/java/examples/BasicExample.java	/^  public static void method2($/;"	mthd	file:	class:BasicExample
+method3	src/test/java/examples/BasicExample.java	/^      void method3() {}$/;"	mthd	class:InnerClass
 method4	src/test/java/examples/BasicExample.java	/^      private void method4() {}$/;"	mthd	class:InnerClass