test: add performance and improve snapshot testing

Add `DiffLayouterPerformanceTests.swift` to test text layout
performance with varying word counts. Convert existing snapshot tests
to use XCTest, enhancing compatibility and extendability. Introduce
snapshot artifacts directory configuration to manage artifacts. Update
tests to specify the snapshot test name explicitly. Modify
`verticalInsetIsNonNegativeAndMonotonic` test to ensure non-negativity
and check monotonicity of vertical insets, improving test rigor.

Author: iSapozhnik

.gitignore

@@ -6,3 +6,4 @@ DerivedData/
 .swiftpm/configuration/registries.json
 .swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata
 .netrc
+.snapshot-artifacts/

Tests/TextDiffTests/DiffLayouterPerformanceTests.swift

@@ -0,0 +1,62 @@
+import AppKit
+import XCTest
+@testable import TextDiff
+
+// swift test --filter DiffLayouterPerformanceTests 2>&1 | xcsift
+
+final class DiffLayouterPerformanceTests: XCTestCase {
+    func testLayoutPerformance200Words() {
+        runLayoutPerformanceTest(wordCount: 200)
+    }
+
+    func testLayoutPerformance500Words() {
+        runLayoutPerformanceTest(wordCount: 500)
+    }
+
+    func testLayoutPerformance1000Words() {
+        runLayoutPerformanceTest(wordCount: 1000)
+    }
+
+    private func runLayoutPerformanceTest(wordCount: Int) {
+        let style = TextDiffStyle.default
+        let verticalInset = DiffTextLayoutMetrics.verticalTextInset(for: style)
+        let contentInsets = NSEdgeInsets(top: verticalInset, left: 0, bottom: verticalInset, right: 0)
+        let availableWidth: CGFloat = 520
+
+        let original = Self.largeText(wordCount: wordCount)
+        let updated = Self.replacingLastWord(in: original)
+        let segments = TextDiffEngine.diff(original: original, updated: updated, mode: .character)
+
+        measure(metrics: [XCTClockMetric()]) {
+            let layout = DiffTokenLayouter.layout(
+                segments: segments,
+                style: style,
+                availableWidth: availableWidth,
+                contentInsets: contentInsets
+            )
+            XCTAssertFalse(layout.runs.isEmpty)
+        }
+    }
+
+    private static func largeText(wordCount: Int) -> String {
+        let vocabulary = [
+            "alpha", "beta", "gamma", "delta", "epsilon", "theta", "lambda", "sigma",
+            "swift", "layout", "render", "token", "word", "segment", "measure", "width"
+        ]
+        var words: [String] = []
+        words.reserveCapacity(wordCount)
+
+        for index in 0..<wordCount {
+            words.append(vocabulary[index % vocabulary.count])
+        }
+
+        return words.joined(separator: " ")
+    }
+
+    private static func replacingLastWord(in text: String) -> String {
+        guard let lastSpace = text.lastIndex(of: " ") else {
+            return "changed"
+        }
+        return String(text[..<lastSpace]) + " changed"
+    }
+}

Tests/TextDiffTests/NSTextDiffSnapshotTests.swift

@@ -1,53 +1,61 @@
 import AppKit
 import SnapshotTesting
-import Testing
 import TextDiff
+import XCTest
 
-@Suite(.snapshots(record: .missing))
-@MainActor
-struct NSTextDiffSnapshotTests {
-    @Test
-    func token_basic_replacement() {
+final class NSTextDiffSnapshotTests: XCTestCase {
+    override func invokeTest() {
+        withSnapshotTesting(record: .missing) {
+            super.invokeTest()
+        }
+    }
+
+    @MainActor
+    func testTokenBasicReplacement() {
         assertNSTextDiffSnapshot(
             original: "Apply old value in this sentence.",
             updated: "Apply new value in this sentence.",
             mode: .token,
-            size: CGSize(width: 500, height: 120)
+            size: CGSize(width: 500, height: 120),
+            testName: "token_basic_replacement()"
         )
     }
 
-    @Test
-    func character_suffix_refinement() {
+    @MainActor
+    func testCharacterSuffixRefinement() {
         assertNSTextDiffSnapshot(
             original: "Add a diff",
             updated: "Added a diff",
             mode: .character,
-            size: CGSize(width: 320, height: 110)
+            size: CGSize(width: 320, height: 110),
+            testName: "character_suffix_refinement()"
         )
     }
 
-    @Test
-    func punctuation_replacement() {
+    @MainActor
+    func testPunctuationReplacement() {
         assertNSTextDiffSnapshot(
             original: "Wait!",
             updated: "Wait.",
             mode: .token,
-            size: CGSize(width: 320, height: 100)
+            size: CGSize(width: 320, height: 100),
+            testName: "punctuation_replacement()"
         )
     }
 
-    @Test
-    func multiline_insertion_wrap() {
+    @MainActor
+    func testMultilineInsertionWrap() {
         assertNSTextDiffSnapshot(
             original: "line1\nline2",
             updated: "line1\nlineX\nline2",
             mode: .token,
-            size: CGSize(width: 300, height: 150)
+            size: CGSize(width: 300, height: 150),
+            testName: "multiline_insertion_wrap()"
         )
     }
 
-    @Test
-    func custom_style_spacing_strikethrough() {
+    @MainActor
+    func testCustomStyleSpacingStrikethrough() {
         var style = TextDiffStyle.default
         style.removalsStyle.strikethrough = true
         style.interChipSpacing = 1
@@ -57,7 +65,8 @@ struct NSTextDiffSnapshotTests {
             updated: sampleUpdatedSentence,
             mode: .character,
             style: style,
-            size: CGSize(width: 300, height: 180)
+            size: CGSize(width: 300, height: 180),
+            testName: "custom_style_spacing_strikethrough()"
         )
     }
 

Tests/TextDiffTests/SnapshotTestSupport.swift

@@ -20,6 +20,8 @@ func assertTextDiffSnapshot(
     line: UInt = #line,
     column: UInt = #column
 ) {
+    configureSnapshotArtifactsDirectory(filePath: filePath)
+
     let rootView = TextDiffView(
         original: original,
         updated: updated,
@@ -36,19 +38,21 @@ func assertTextDiffSnapshot(
 
     let snapshotImage = renderSnapshotImage1x(view: hostingView, size: size)
 
-    assertSnapshot(
-        of: snapshotImage,
-        as: .image(
-            precision: snapshotPrecision,
-            perceptualPrecision: snapshotPerceptualPrecision
-        ),
-        named: name,
-        fileID: fileID,
-        file: filePath,
-        testName: testName,
-        line: line,
-        column: column
-    )
+    withSnapshotTesting(diffTool: .ksdiff) {
+        assertSnapshot(
+            of: snapshotImage,
+            as: .image(
+                precision: snapshotPrecision,
+                perceptualPrecision: snapshotPerceptualPrecision
+            ),
+            named: name,
+            fileID: fileID,
+            file: filePath,
+            testName: testName,
+            line: line,
+            column: column
+        )
+    }
 }
 
 @MainActor
@@ -65,6 +69,8 @@ func assertNSTextDiffSnapshot(
     line: UInt = #line,
     column: UInt = #column
 ) {
+    configureSnapshotArtifactsDirectory(filePath: filePath)
+
     let diffView = NSTextDiffView(
         original: original,
         updated: updated,
@@ -84,19 +90,31 @@ func assertNSTextDiffSnapshot(
 
     let snapshotImage = renderSnapshotImage1x(view: container, size: size)
 
-    assertSnapshot(
-        of: snapshotImage,
-        as: .image(
-            precision: snapshotPrecision,
-            perceptualPrecision: snapshotPerceptualPrecision
-        ),
-        named: name,
-        fileID: fileID,
-        file: filePath,
-        testName: testName,
-        line: line,
-        column: column
-    )
+    withSnapshotTesting(diffTool: .ksdiff) {
+        assertSnapshot(
+            of: snapshotImage,
+            as: .image(
+                precision: snapshotPrecision,
+                perceptualPrecision: snapshotPerceptualPrecision
+            ),
+            named: name,
+            fileID: fileID,
+            file: filePath,
+            testName: testName,
+            line: line,
+            column: column
+        )
+    }
+}
+
+private func configureSnapshotArtifactsDirectory(filePath: StaticString) {
+    let fileURL = URL(fileURLWithPath: "\(filePath)")
+    let repoRootURL = fileURL
+        .deletingLastPathComponent() // TextDiffTests
+        .deletingLastPathComponent() // Tests
+        .deletingLastPathComponent() // repo root
+    let artifactsPath = repoRootURL.appendingPathComponent(".snapshot-artifacts", isDirectory: true).path
+    setenv("SNAPSHOT_ARTIFACTS", artifactsPath, 1)
 }
 
 @MainActor

Tests/TextDiffTests/TextDiffEngineTests.swift

@@ -332,12 +332,21 @@ func layouterUsesRemovalStrikethroughFromRemovalStyle() throws {
 }
 
 @Test
-func verticalInsetScalesWithChipInsets() {
-    #expect(DiffTextLayoutMetrics.verticalTextInset(for: .default) == 3)
-
-    var style = TextDiffStyle.default
-    style.chipInsets = NSEdgeInsets(top: 6, left: 2, bottom: 1, right: 2)
-    #expect(DiffTextLayoutMetrics.verticalTextInset(for: style) == 8)
+func verticalInsetIsNonNegativeAndMonotonic() {
+    var base = TextDiffStyle.default
+    base.chipInsets = NSEdgeInsets(top: 0, left: 2, bottom: 0, right: 2)
+    let baseInset = DiffTextLayoutMetrics.verticalTextInset(for: base)
+    #expect(baseInset >= 0)
+
+    var largerTop = base
+    largerTop.chipInsets = NSEdgeInsets(top: 6, left: 2, bottom: 0, right: 2)
+    let largerTopInset = DiffTextLayoutMetrics.verticalTextInset(for: largerTop)
+    #expect(largerTopInset >= baseInset)
+
+    var largerBottom = base
+    largerBottom.chipInsets = NSEdgeInsets(top: 0, left: 2, bottom: 7, right: 2)
+    let largerBottomInset = DiffTextLayoutMetrics.verticalTextInset(for: largerBottom)
+    #expect(largerBottomInset >= baseInset)
 }
 
 @Test