diff --git a/Tests/TUIkitTests/ComponentViewTests.swift b/Tests/TUIkitTests/ComponentViewTests.swift
new file mode 100644
index 0000000..66fbda3
--- /dev/null
+++ b/Tests/TUIkitTests/ComponentViewTests.swift
@@ -0,0 +1,417 @@
+//
+//  ComponentViewTests.swift
+//  TUIkit
+//
+//  Tests for Box, Card, Panel, ContainerConfig, ContainerView, and ForEach views.
+//
+
+import Testing
+
+@testable import TUIkit
+
+// MARK: - Test Helpers
+
+/// Creates a default render context for testing.
+private func testContext(width: Int = 40, height: Int = 24) -> RenderContext {
+    RenderContext(availableWidth: width, availableHeight: height)
+}
+
+// MARK: - Box Tests
+
+@Suite("Box Tests")
+struct BoxTests {
+
+    @Test("Box can be created with default style")
+    func boxDefaultCreation() {
+        let box = Box {
+            Text("Hello")
+        }
+        #expect(box.borderStyle == nil)
+        #expect(box.borderColor == nil)
+    }
+
+    @Test("Box can be created with explicit border style")
+    func boxExplicitStyle() {
+        let box = Box(.doubleLine, color: .cyan) {
+            Text("Styled")
+        }
+        #expect(box.borderStyle == .doubleLine)
+        #expect(box.borderColor == .cyan)
+    }
+
+    @Test("Box renders with border around content")
+    func boxRendersWithBorder() {
+        let box = Box(.line) {
+            Text("Hi")
+        }
+        let context = testContext()
+        let buffer = renderToBuffer(box, context: context)
+
+        // Box = border top + content + border bottom = 3 lines minimum
+        #expect(buffer.height >= 3)
+        // Width = content width + 2 (left + right border)
+        #expect(buffer.width >= 4) // "Hi" (2) + borders (2)
+    }
+
+    @Test("Box renders empty content")
+    func boxEmptyContent() {
+        let box = Box(.line) {
+            EmptyView()
+        }
+        let context = testContext()
+        let buffer = renderToBuffer(box, context: context)
+
+        // EmptyView produces empty buffer, so bordered empty = empty
+        #expect(buffer.isEmpty)
+    }
+
+    @Test("Box with multiple children renders vertically")
+    func boxMultipleChildren() {
+        let box = Box(.line) {
+            Text("Line 1")
+            Text("Line 2")
+        }
+        let context = testContext()
+        let buffer = renderToBuffer(box, context: context)
+
+        // Top border + 2 content lines + bottom border = 4
+        #expect(buffer.height >= 4)
+    }
+
+    @Test("Box delegates to body (is composite, not Renderable)")
+    func boxIsComposite() {
+        let box = Box {
+            Text("Test")
+        }
+        // Box should NOT conform to Renderable — it uses body
+        #expect(!(box is Renderable))
+    }
+}
+
+// MARK: - Card Tests
+
+@Suite("Card Tests")
+struct CardTests {
+
+    @Test("Card can be created without title")
+    func cardNoTitle() {
+        let card = Card {
+            Text("Content")
+        }
+        #expect(card.title == nil)
+        #expect(card.footer == nil)
+        #expect(card.backgroundColor == nil)
+    }
+
+    @Test("Card can be created with title")
+    func cardWithTitle() {
+        let card = Card(title: "My Card") {
+            Text("Content")
+        }
+        #expect(card.title == "My Card")
+    }
+
+    @Test("Card can be created with footer")
+    func cardWithFooter() {
+        let card = Card(title: "Info") {
+            Text("Body")
+        } footer: {
+            Text("Footer")
+        }
+        #expect(card.title == "Info")
+        #expect(card.footer != nil)
+    }
+
+    @Test("Card can be created with custom border style")
+    func cardCustomStyle() {
+        let card = Card(
+            title: "Styled",
+            borderStyle: .doubleLine,
+            borderColor: .cyan,
+            titleColor: .brightYellow,
+            backgroundColor: .blue
+        ) {
+            Text("Content")
+        }
+        #expect(card.title == "Styled")
+        #expect(card.config.borderStyle == .doubleLine)
+        #expect(card.config.borderColor == .cyan)
+        #expect(card.config.titleColor == .brightYellow)
+        #expect(card.backgroundColor == .blue)
+    }
+
+    @Test("Card renders with border")
+    func cardRenders() {
+        let card = Card(title: "Test") {
+            Text("Hello")
+        }
+        let context = testContext()
+        let buffer = card.renderToBuffer(context: context)
+
+        // Should have top border + content + bottom border
+        #expect(buffer.height >= 3)
+        #expect(!buffer.isEmpty)
+    }
+
+    @Test("Card without title renders")
+    func cardNoTitleRenders() {
+        let card = Card {
+            Text("Content")
+        }
+        let context = testContext()
+        let buffer = card.renderToBuffer(context: context)
+
+        #expect(buffer.height >= 3)
+        #expect(!buffer.isEmpty)
+    }
+
+    @Test("Card with footer is taller than without")
+    func cardFooterAddsHeight() {
+        let cardWithout = Card(title: "Test") {
+            Text("Body")
+        }
+        let cardWith = Card(title: "Test") {
+            Text("Body")
+        } footer: {
+            Text("Footer")
+        }
+        let context = testContext()
+
+        let bufferWithout = cardWithout.renderToBuffer(context: context)
+        let bufferWith = cardWith.renderToBuffer(context: context)
+
+        #expect(bufferWith.height > bufferWithout.height)
+    }
+
+    @Test("Card conforms to Renderable")
+    func cardIsRenderable() {
+        let card = Card { Text("Test") }
+        #expect(card is Renderable)
+    }
+}
+
+// MARK: - Panel Tests
+
+@Suite("Panel Tests")
+struct PanelTests {
+
+    @Test("Panel can be created with title")
+    func panelCreation() {
+        let panel = Panel("Settings") {
+            Text("Option 1")
+        }
+        #expect(panel.title == "Settings")
+        #expect(panel.footer == nil)
+    }
+
+    @Test("Panel can be created with footer")
+    func panelWithFooter() {
+        let panel = Panel("Info") {
+            Text("Content")
+        } footer: {
+            Text("Done")
+        }
+        #expect(panel.title == "Info")
+        #expect(panel.footer != nil)
+    }
+
+    @Test("Panel can be created with custom style")
+    func panelCustomStyle() {
+        let panel = Panel(
+            "Styled",
+            borderStyle: .heavy,
+            borderColor: .red,
+            titleColor: .yellow
+        ) {
+            Text("Content")
+        }
+        #expect(panel.config.borderStyle == .heavy)
+        #expect(panel.config.borderColor == .red)
+        #expect(panel.config.titleColor == .yellow)
+    }
+
+    @Test("Panel renders with border and title")
+    func panelRenders() {
+        let panel = Panel("Test Panel") {
+            Text("Hello")
+        }
+        let context = testContext()
+        let buffer = panel.renderToBuffer(context: context)
+
+        // Top border (with title) + content + bottom border
+        #expect(buffer.height >= 3)
+        #expect(!buffer.isEmpty)
+    }
+
+    @Test("Panel with footer is taller")
+    func panelFooterAddsHeight() {
+        let panelWithout = Panel("Test") {
+            Text("Body")
+        }
+        let panelWith = Panel("Test") {
+            Text("Body")
+        } footer: {
+            Text("Footer")
+        }
+        let context = testContext()
+
+        let bufferWithout = panelWithout.renderToBuffer(context: context)
+        let bufferWith = panelWith.renderToBuffer(context: context)
+
+        #expect(bufferWith.height > bufferWithout.height)
+    }
+
+    @Test("Panel conforms to Renderable")
+    func panelIsRenderable() {
+        let panel = Panel("Title") { Text("Content") }
+        #expect(panel is Renderable)
+    }
+
+    @Test("Panel default padding is horizontal only")
+    func panelDefaultPadding() {
+        let panel = Panel("Test") {
+            Text("Content")
+        }
+        #expect(panel.config.padding.leading == 1)
+        #expect(panel.config.padding.trailing == 1)
+        #expect(panel.config.padding.top == 0)
+        #expect(panel.config.padding.bottom == 0)
+    }
+}
+
+// MARK: - ContainerConfig Tests
+
+@Suite("ContainerConfig Tests")
+struct ContainerConfigTests {
+
+    @Test("Default config has expected values")
+    func defaultConfig() {
+        let config = ContainerConfig.default
+        #expect(config.borderStyle == nil)
+        #expect(config.borderColor == nil)
+        #expect(config.titleColor == nil)
+        #expect(config.padding.leading == 1)
+        #expect(config.padding.trailing == 1)
+        #expect(config.showFooterSeparator == true)
+    }
+
+    @Test("Custom config stores all values")
+    func customConfig() {
+        let config = ContainerConfig(
+            borderStyle: .doubleLine,
+            borderColor: .cyan,
+            titleColor: .yellow,
+            padding: EdgeInsets(all: 2),
+            showFooterSeparator: false
+        )
+        #expect(config.borderStyle == .doubleLine)
+        #expect(config.borderColor == .cyan)
+        #expect(config.titleColor == .yellow)
+        #expect(config.padding.top == 2)
+        #expect(config.padding.leading == 2)
+        #expect(config.showFooterSeparator == false)
+    }
+}
+
+// MARK: - ContainerView Tests
+
+@Suite("ContainerView Direct Tests")
+struct ContainerViewDirectTests {
+
+    @Test("ContainerView can be created without title")
+    func containerViewNoTitle() {
+        let container = ContainerView {
+            Text("Content")
+        }
+        #expect(container.title == nil)
+        #expect(container.footer == nil)
+    }
+
+    @Test("ContainerView can be created with title and footer")
+    func containerViewWithTitleAndFooter() {
+        let container = ContainerView(title: "Header") {
+            Text("Body")
+        } footer: {
+            Text("Footer")
+        }
+        #expect(container.title == "Header")
+        #expect(container.footer != nil)
+    }
+
+    @Test("ContainerView renders with border")
+    func containerViewRenders() {
+        let container = ContainerView(title: "Test") {
+            Text("Content")
+        }
+        let context = testContext()
+        let buffer = container.renderToBuffer(context: context)
+
+        #expect(buffer.height >= 3)
+        #expect(!buffer.isEmpty)
+    }
+
+    @Test("ContainerView conforms to Renderable")
+    func containerViewIsRenderable() {
+        let container = ContainerView { Text("Test") }
+        #expect(container is Renderable)
+    }
+}
+
+// MARK: - ForEach Tests
+
+@Suite("ForEach Tests")
+struct ForEachTests {
+
+    struct TestItem: Identifiable {
+        let id: String
+        let name: String
+    }
+
+    @Test("ForEach can be created with Identifiable data")
+    func forEachIdentifiable() {
+        let items = [TestItem(id: "1", name: "One"), TestItem(id: "2", name: "Two")]
+        let forEach = ForEach(items) { item in
+            Text(item.name)
+        }
+        #expect(forEach.data.count == 2)
+    }
+
+    @Test("ForEach can be created with explicit ID key path")
+    func forEachExplicitId() {
+        let names = ["Anna", "Bob", "Clara"]
+        let forEach = ForEach(names, id: \.self) { name in
+            Text(name)
+        }
+        #expect(forEach.data.count == 3)
+    }
+
+    @Test("ForEach can be created with Range")
+    func forEachRange() {
+        let forEach = ForEach(0..<5) { index in
+            Text("Item \(index)")
+        }
+        #expect(forEach.data.count == 5)
+    }
+
+    @Test("ForEach generates correct number of views")
+    func forEachViewGeneration() {
+        let items = [TestItem(id: "a", name: "Alpha"), TestItem(id: "b", name: "Beta")]
+        let forEach = ForEach(items) { item in
+            Text(item.name)
+        }
+
+        // Verify content closure works
+        var generatedTexts: [String] = []
+        for item in forEach.data {
+            let view = forEach.content(item)
+            generatedTexts.append(view.content)
+        }
+        #expect(generatedTexts == ["Alpha", "Beta"])
+    }
+
+    // NOTE: ForEach inside VStack/HStack cannot be tested via renderToBuffer
+    // directly. ForEach is flattened into ViewArray by @ViewBuilder.buildArray
+    // at compile time — not at render time. Direct construction in tests
+    // bypasses the builder, so ForEach remains unflattened and produces
+    // an empty buffer. This is expected behavior, matching SwiftUI's pattern.
+}
diff --git a/Tests/TUIkitTests/ModifierTests.swift b/Tests/TUIkitTests/ModifierTests.swift
new file mode 100644
index 0000000..62ff0f8
--- /dev/null
+++ b/Tests/TUIkitTests/ModifierTests.swift
@@ -0,0 +1,620 @@
+//
+//  ModifierTests.swift
+//  TUIkit
+//
+//  Tests for Frame, Padding, Border, and Background modifiers.
+//
+
+import Testing
+
+@testable import TUIkit
+
+// MARK: - Test Helpers
+
+/// Creates a default render context for testing.
+private func testContext(width: Int = 40, height: Int = 24) -> RenderContext {
+    RenderContext(availableWidth: width, availableHeight: height)
+}
+
+// MARK: - EdgeInsets Tests
+
+@Suite("EdgeInsets Tests")
+struct EdgeInsetsTests {
+
+    @Test("EdgeInsets individual values")
+    func edgeInsetsIndividual() {
+        let insets = EdgeInsets(top: 1, leading: 2, bottom: 3, trailing: 4)
+        #expect(insets.top == 1)
+        #expect(insets.leading == 2)
+        #expect(insets.bottom == 3)
+        #expect(insets.trailing == 4)
+    }
+
+    @Test("EdgeInsets uniform value")
+    func edgeInsetsUniform() {
+        let insets = EdgeInsets(all: 3)
+        #expect(insets.top == 3)
+        #expect(insets.leading == 3)
+        #expect(insets.bottom == 3)
+        #expect(insets.trailing == 3)
+    }
+
+    @Test("EdgeInsets horizontal and vertical")
+    func edgeInsetsHorizontalVertical() {
+        let insets = EdgeInsets(horizontal: 2, vertical: 1)
+        #expect(insets.top == 1)
+        #expect(insets.leading == 2)
+        #expect(insets.bottom == 1)
+        #expect(insets.trailing == 2)
+    }
+
+    @Test("EdgeInsets default values are zero")
+    func edgeInsetsDefaults() {
+        let insets = EdgeInsets()
+        #expect(insets.top == 0)
+        #expect(insets.leading == 0)
+        #expect(insets.bottom == 0)
+        #expect(insets.trailing == 0)
+    }
+
+    @Test("EdgeInsets is Equatable")
+    func edgeInsetsEquatable() {
+        let insetsA = EdgeInsets(all: 2)
+        let insetsB = EdgeInsets(top: 2, leading: 2, bottom: 2, trailing: 2)
+        #expect(insetsA == insetsB)
+    }
+}
+
+// MARK: - Edge Tests
+
+@Suite("Edge Tests")
+struct EdgeTests {
+
+    @Test("Individual edges exist")
+    func individualEdges() {
+        #expect(Edge.top.rawValue == 1)
+        #expect(Edge.leading.rawValue == 2)
+        #expect(Edge.bottom.rawValue == 4)
+        #expect(Edge.trailing.rawValue == 8)
+    }
+
+    @Test("Edge.all contains all edges")
+    func edgeAll() {
+        #expect(Edge.all.contains(.top))
+        #expect(Edge.all.contains(.leading))
+        #expect(Edge.all.contains(.bottom))
+        #expect(Edge.all.contains(.trailing))
+    }
+
+    @Test("Edge.horizontal contains leading and trailing")
+    func edgeHorizontal() {
+        #expect(Edge.horizontal.contains(.leading))
+        #expect(Edge.horizontal.contains(.trailing))
+        #expect(!Edge.horizontal.contains(.top))
+        #expect(!Edge.horizontal.contains(.bottom))
+    }
+
+    @Test("Edge.vertical contains top and bottom")
+    func edgeVertical() {
+        #expect(Edge.vertical.contains(.top))
+        #expect(Edge.vertical.contains(.bottom))
+        #expect(!Edge.vertical.contains(.leading))
+        #expect(!Edge.vertical.contains(.trailing))
+    }
+}
+
+// MARK: - PaddingModifier Tests
+
+@Suite("PaddingModifier Tests")
+struct PaddingModifierTests {
+
+    @Test("Padding adds empty lines for top and bottom")
+    func paddingTopBottom() {
+        let modifier = PaddingModifier(insets: EdgeInsets(top: 1, leading: 0, bottom: 1, trailing: 0))
+        let buffer = FrameBuffer(lines: ["Hello"])
+        let context = testContext()
+
+        let result = modifier.modify(buffer: buffer, context: context)
+
+        // 1 top + 1 content + 1 bottom = 3
+        #expect(result.height == 3)
+        #expect(result.lines[0].trimmingCharacters(in: .whitespaces) == "")
+        #expect(result.lines[1] == "Hello")
+        #expect(result.lines[2].trimmingCharacters(in: .whitespaces) == "")
+    }
+
+    @Test("Padding adds spaces for leading and trailing")
+    func paddingLeadingTrailing() {
+        let modifier = PaddingModifier(insets: EdgeInsets(top: 0, leading: 2, bottom: 0, trailing: 3))
+        let buffer = FrameBuffer(lines: ["Hi"])
+        let context = testContext()
+
+        let result = modifier.modify(buffer: buffer, context: context)
+
+        #expect(result.height == 1)
+        // "  Hi   " — 2 leading + "Hi" + 3 trailing
+        #expect(result.lines[0] == "  Hi   ")
+    }
+
+    @Test("Padding all sides")
+    func paddingAllSides() {
+        let modifier = PaddingModifier(insets: EdgeInsets(all: 1))
+        let buffer = FrameBuffer(lines: ["X"])
+        let context = testContext()
+
+        let result = modifier.modify(buffer: buffer, context: context)
+
+        // 1 top + 1 content + 1 bottom = 3
+        #expect(result.height == 3)
+        // Content line: 1 leading + "X" + 1 trailing = " X "
+        #expect(result.lines[1] == " X ")
+    }
+
+    @Test("Padding on empty buffer returns empty")
+    func paddingEmptyBuffer() {
+        let modifier = PaddingModifier(insets: EdgeInsets(all: 2))
+        let buffer = FrameBuffer()
+        let context = testContext()
+
+        let result = modifier.modify(buffer: buffer, context: context)
+
+        // Only padding lines (no content)
+        #expect(result.height == 4) // 2 top + 0 content + 2 bottom
+    }
+
+    @Test("Padding preserves multiple content lines")
+    func paddingMultipleLines() {
+        let modifier = PaddingModifier(insets: EdgeInsets(top: 1, leading: 1, bottom: 1, trailing: 1))
+        let buffer = FrameBuffer(lines: ["AAA", "BBB"])
+        let context = testContext()
+
+        let result = modifier.modify(buffer: buffer, context: context)
+
+        // 1 top + 2 content + 1 bottom = 4
+        #expect(result.height == 4)
+        #expect(result.lines[1] == " AAA ")
+        #expect(result.lines[2] == " BBB ")
+    }
+
+    @Test("Zero padding returns original dimensions")
+    func paddingZero() {
+        let modifier = PaddingModifier(insets: EdgeInsets())
+        let buffer = FrameBuffer(lines: ["Test"])
+        let context = testContext()
+
+        let result = modifier.modify(buffer: buffer, context: context)
+
+        #expect(result.height == 1)
+        #expect(result.lines[0] == "Test")
+    }
+}
+
+// MARK: - FrameModifier Tests
+
+@Suite("FrameModifier Tests")
+struct FrameModifierTests {
+
+    @Test("FrameDimension.fixed stores value")
+    func frameDimensionFixed() {
+        let dim = FrameDimension.fixed(10)
+        #expect(dim == .fixed(10))
+    }
+
+    @Test("FrameDimension.infinity and .max are equal")
+    func frameDimensionInfinity() {
+        #expect(FrameDimension.infinity == .max)
+    }
+
+    @Test("FlexibleFrameView with maxWidth infinity fills available width")
+    func frameMaxWidthInfinity() {
+        let frame = FlexibleFrameView(
+            content: Text("Hi"),
+            minWidth: nil,
+            idealWidth: nil,
+            maxWidth: .infinity,
+            minHeight: nil,
+            idealHeight: nil,
+            maxHeight: nil,
+            alignment: .center
+        )
+        let context = testContext(width: 30)
+        let buffer = frame.renderToBuffer(context: context)
+
+        #expect(buffer.width == 30)
+    }
+
+    @Test("FlexibleFrameView with fixed maxWidth constrains")
+    func frameFixedMaxWidth() {
+        let frame = FlexibleFrameView(
+            content: Text("Short"),
+            minWidth: nil,
+            idealWidth: nil,
+            maxWidth: .fixed(10),
+            minHeight: nil,
+            idealHeight: nil,
+            maxHeight: nil,
+            alignment: .leading
+        )
+        let context = testContext(width: 40)
+        let buffer = frame.renderToBuffer(context: context)
+
+        // Content "Short" is 5 chars, no maxWidth expansion without infinity
+        #expect(buffer.width <= 10)
+    }
+
+    @Test("FlexibleFrameView with minWidth enforces minimum")
+    func frameMinWidth() {
+        let frame = FlexibleFrameView(
+            content: Text("Hi"),
+            minWidth: 10,
+            idealWidth: nil,
+            maxWidth: nil,
+            minHeight: nil,
+            idealHeight: nil,
+            maxHeight: nil,
+            alignment: .leading
+        )
+        let context = testContext(width: 40)
+        let buffer = frame.renderToBuffer(context: context)
+
+        #expect(buffer.width >= 10)
+    }
+
+    @Test("FlexibleFrameView with minHeight enforces minimum")
+    func frameMinHeight() {
+        let frame = FlexibleFrameView(
+            content: Text("Hi"),
+            minWidth: nil,
+            idealWidth: nil,
+            maxWidth: nil,
+            minHeight: 5,
+            idealHeight: nil,
+            maxHeight: nil,
+            alignment: .top
+        )
+        let context = testContext()
+        let buffer = frame.renderToBuffer(context: context)
+
+        #expect(buffer.height >= 5)
+    }
+
+    @Test("FlexibleFrameView alignment center")
+    func frameCenterAlignment() {
+        let frame = FlexibleFrameView(
+            content: Text("Hi"),
+            minWidth: 10,
+            idealWidth: nil,
+            maxWidth: nil,
+            minHeight: 3,
+            idealHeight: nil,
+            maxHeight: nil,
+            alignment: .center
+        )
+        let context = testContext()
+        let buffer = frame.renderToBuffer(context: context)
+
+        #expect(buffer.width >= 10)
+        #expect(buffer.height >= 3)
+        // Center vertically: content should be on line 1 (middle of 3)
+        let contentLine = buffer.lines[1]
+        #expect(contentLine.contains("Hi"))
+    }
+
+    @Test("FlexibleFrameView alignment trailing")
+    func frameTrailingAlignment() {
+        let frame = FlexibleFrameView(
+            content: Text("Hi"),
+            minWidth: 10,
+            idealWidth: nil,
+            maxWidth: nil,
+            minHeight: nil,
+            idealHeight: nil,
+            maxHeight: nil,
+            alignment: .trailing
+        )
+        let context = testContext()
+        let buffer = frame.renderToBuffer(context: context)
+
+        // "Hi" should be right-aligned within 10 chars
+        let line = buffer.lines[0]
+        #expect(line.hasSuffix("Hi"))
+    }
+
+    @Test("FlexibleFrameView alignment bottom")
+    func frameBottomAlignment() {
+        let frame = FlexibleFrameView(
+            content: Text("Hi"),
+            minWidth: nil,
+            idealWidth: nil,
+            maxWidth: nil,
+            minHeight: 3,
+            idealHeight: nil,
+            maxHeight: nil,
+            alignment: .bottom
+        )
+        let context = testContext()
+        let buffer = frame.renderToBuffer(context: context)
+
+        #expect(buffer.height >= 3)
+        // Content on last line
+        let lastLine = buffer.lines[buffer.height - 1]
+        #expect(lastLine.contains("Hi"))
+    }
+
+    @Test("FlexibleFrameView conforms to Renderable")
+    func frameIsRenderable() {
+        let frame = FlexibleFrameView(
+            content: Text("Test"),
+            minWidth: nil, idealWidth: nil, maxWidth: nil,
+            minHeight: nil, idealHeight: nil, maxHeight: nil,
+            alignment: .center
+        )
+        #expect(frame is Renderable)
+    }
+}
+
+// MARK: - BorderModifier Tests
+
+@Suite("BorderModifier Tests")
+struct BorderModifierTests {
+
+    @Test("BorderedView can be created")
+    func borderedViewCreation() {
+        let bordered = BorderedView(content: Text("Hi"), style: .line, color: .green)
+        #expect(bordered.style == .line)
+        #expect(bordered.color == .green)
+    }
+
+    @Test("BorderedView renders with top and bottom borders")
+    func borderedViewRenders() {
+        let bordered = BorderedView(content: Text("Test"), style: .line, color: nil)
+        let context = testContext()
+        let buffer = bordered.renderToBuffer(context: context)
+
+        // Top border + content + bottom border
+        #expect(buffer.height == 3)
+        #expect(!buffer.isEmpty)
+    }
+
+    @Test("BorderedView with empty content returns empty")
+    func borderedViewEmptyContent() {
+        let bordered = BorderedView(content: EmptyView(), style: .line, color: nil)
+        let context = testContext()
+        let buffer = bordered.renderToBuffer(context: context)
+
+        #expect(buffer.isEmpty)
+    }
+
+    @Test("BorderedView with line style uses correct corner characters")
+    func borderedViewLineStyle() {
+        let bordered = BorderedView(content: Text("X"), style: .line, color: nil)
+        let context = testContext()
+        let buffer = bordered.renderToBuffer(context: context)
+
+        let topLine = buffer.lines[0].stripped
+        let bottomLine = buffer.lines[buffer.height - 1].stripped
+
+        #expect(topLine.hasPrefix("┌"))
+        #expect(topLine.hasSuffix("┐"))
+        #expect(bottomLine.hasPrefix("└"))
+        #expect(bottomLine.hasSuffix("┘"))
+    }
+
+    @Test("BorderedView with doubleLine style uses correct characters")
+    func borderedViewDoubleLineStyle() {
+        let bordered = BorderedView(content: Text("X"), style: .doubleLine, color: nil)
+        let context = testContext()
+        let buffer = bordered.renderToBuffer(context: context)
+
+        let topLine = buffer.lines[0].stripped
+        let bottomLine = buffer.lines[buffer.height - 1].stripped
+
+        #expect(topLine.hasPrefix("╔"))
+        #expect(topLine.hasSuffix("╗"))
+        #expect(bottomLine.hasPrefix("╚"))
+        #expect(bottomLine.hasSuffix("╝"))
+    }
+
+    @Test("BorderedView with rounded style uses correct characters")
+    func borderedViewRoundedStyle() {
+        let bordered = BorderedView(content: Text("X"), style: .rounded, color: nil)
+        let context = testContext()
+        let buffer = bordered.renderToBuffer(context: context)
+
+        let topLine = buffer.lines[0].stripped
+        let bottomLine = buffer.lines[buffer.height - 1].stripped
+
+        #expect(topLine.hasPrefix("╭"))
+        #expect(topLine.hasSuffix("╮"))
+        #expect(bottomLine.hasPrefix("╰"))
+        #expect(bottomLine.hasSuffix("╯"))
+    }
+
+    @Test("BorderedView with heavy style uses correct characters")
+    func borderedViewHeavyStyle() {
+        let bordered = BorderedView(content: Text("X"), style: .heavy, color: nil)
+        let context = testContext()
+        let buffer = bordered.renderToBuffer(context: context)
+
+        let topLine = buffer.lines[0].stripped
+        let bottomLine = buffer.lines[buffer.height - 1].stripped
+
+        #expect(topLine.hasPrefix("┏"))
+        #expect(topLine.hasSuffix("┓"))
+        #expect(bottomLine.hasPrefix("┗"))
+        #expect(bottomLine.hasSuffix("┛"))
+    }
+
+    @Test("BorderedView with ascii style uses correct characters")
+    func borderedViewAsciiStyle() {
+        let bordered = BorderedView(content: Text("X"), style: .ascii, color: nil)
+        let context = testContext()
+        let buffer = bordered.renderToBuffer(context: context)
+
+        let topLine = buffer.lines[0].stripped
+        let bottomLine = buffer.lines[buffer.height - 1].stripped
+
+        #expect(topLine.hasPrefix("+"))
+        #expect(topLine.hasSuffix("+"))
+        #expect(bottomLine.hasPrefix("+"))
+        #expect(bottomLine.hasSuffix("+"))
+    }
+
+    @Test("BorderedView adds 2 to content width")
+    func borderedViewWidthOverhead() {
+        let bordered = BorderedView(content: Text("ABCDE"), style: .line, color: nil)
+        let context = testContext()
+        let buffer = bordered.renderToBuffer(context: context)
+
+        // Content "ABCDE" = 5, + 2 for borders = 7
+        let topLine = buffer.lines[0].stripped
+        #expect(topLine.count == 7)
+    }
+
+    @Test("BorderedView conforms to Renderable")
+    func borderedViewIsRenderable() {
+        let bordered = BorderedView(content: Text("Test"), style: .line, color: nil)
+        #expect(bordered is Renderable)
+    }
+}
+
+// MARK: - BorderStyle Tests
+
+@Suite("BorderStyle Tests")
+struct BorderStyleTests {
+
+    @Test("Predefined styles exist")
+    func predefinedStyles() {
+        // Just verify they all exist and have distinct characters
+        #expect(BorderStyle.line.topLeft == "┌")
+        #expect(BorderStyle.doubleLine.topLeft == "╔")
+        #expect(BorderStyle.rounded.topLeft == "╭")
+        #expect(BorderStyle.heavy.topLeft == "┏")
+        #expect(BorderStyle.block.topLeft == "▄")
+        #expect(BorderStyle.ascii.topLeft == "+")
+        #expect(BorderStyle.none.topLeft == " ")
+    }
+
+    @Test("Line style has T-junctions")
+    func lineStyleTJunctions() {
+        #expect(BorderStyle.line.leftT == "├")
+        #expect(BorderStyle.line.rightT == "┤")
+    }
+
+    @Test("DoubleLine style has T-junctions")
+    func doubleLineTJunctions() {
+        #expect(BorderStyle.doubleLine.leftT == "╠")
+        #expect(BorderStyle.doubleLine.rightT == "╣")
+    }
+
+    @Test("Heavy style has T-junctions")
+    func heavyTJunctions() {
+        #expect(BorderStyle.heavy.leftT == "┣")
+        #expect(BorderStyle.heavy.rightT == "┫")
+    }
+
+    @Test("BorderStyle is Equatable")
+    func borderStyleEquatable() {
+        #expect(BorderStyle.line == BorderStyle.line)
+        #expect(BorderStyle.line != BorderStyle.doubleLine)
+    }
+
+    @Test("Custom border style stores all characters")
+    func customBorderStyle() {
+        let custom = BorderStyle(
+            topLeft: "A",
+            topRight: "B",
+            bottomLeft: "C",
+            bottomRight: "D",
+            horizontal: "E",
+            vertical: "F",
+            leftT: "G",
+            rightT: "H"
+        )
+        #expect(custom.topLeft == "A")
+        #expect(custom.topRight == "B")
+        #expect(custom.bottomLeft == "C")
+        #expect(custom.bottomRight == "D")
+        #expect(custom.horizontal == "E")
+        #expect(custom.vertical == "F")
+        #expect(custom.leftT == "G")
+        #expect(custom.rightT == "H")
+    }
+
+    @Test("Custom border style defaults T-junctions to vertical")
+    func customBorderStyleDefaultTJunctions() {
+        let custom = BorderStyle(
+            topLeft: "A",
+            topRight: "B",
+            bottomLeft: "C",
+            bottomRight: "D",
+            horizontal: "E",
+            vertical: "F"
+        )
+        #expect(custom.leftT == "F")
+        #expect(custom.rightT == "F")
+    }
+
+    @Test("Block style constants exist")
+    func blockStyleConstants() {
+        #expect(BorderStyle.blockBottomHorizontal == "▀")
+        #expect(BorderStyle.blockFooterSeparator == "▄")
+    }
+}
+
+// MARK: - BackgroundModifier Tests
+
+@Suite("BackgroundModifier Tests")
+struct BackgroundModifierTests {
+
+    @Test("Background modifier applies ANSI background code")
+    func backgroundAppliesCode() {
+        let modifier = BackgroundModifier(color: .red)
+        let buffer = FrameBuffer(lines: ["Hello"])
+        let context = testContext()
+
+        let result = modifier.modify(buffer: buffer, context: context)
+
+        #expect(result.height == 1)
+        // Should contain ANSI escape codes
+        let line = result.lines[0]
+        #expect(line.contains("\u{1B}["))
+        #expect(line.contains("Hello"))
+        // Should end with reset
+        #expect(line.hasSuffix(ANSIRenderer.reset))
+    }
+
+    @Test("Background modifier preserves line count")
+    func backgroundPreservesLineCount() {
+        let modifier = BackgroundModifier(color: .blue)
+        let buffer = FrameBuffer(lines: ["Line 1", "Line 2", "Line 3"])
+        let context = testContext()
+
+        let result = modifier.modify(buffer: buffer, context: context)
+
+        #expect(result.height == 3)
+    }
+
+    @Test("Background modifier on empty buffer returns empty")
+    func backgroundEmptyBuffer() {
+        let modifier = BackgroundModifier(color: .green)
+        let buffer = FrameBuffer()
+        let context = testContext()
+
+        let result = modifier.modify(buffer: buffer, context: context)
+
+        #expect(result.isEmpty)
+    }
+
+    @Test("Background modifier pads lines to full width")
+    func backgroundPadsLines() {
+        let modifier = BackgroundModifier(color: .red)
+        let buffer = FrameBuffer(lines: ["Short", "VeryLongLine"])
+        let context = testContext()
+
+        let result = modifier.modify(buffer: buffer, context: context)
+
+        // Both lines should have the same visible width after padding
+        #expect(result.lines[0].strippedLength == result.lines[1].strippedLength)
+    }
+}
diff --git a/Tests/TUIkitTests/TViewTests.swift b/Tests/TUIkitTests/ViewTests.swift
similarity index 100%
rename from Tests/TUIkitTests/TViewTests.swift
rename to Tests/TUIkitTests/ViewTests.swift