Increment 0: add XCTest target, testing process & 10x value plan

- Add TopManagerTests unit-test target (hosted, @testable import)
- 14 baseline tests for formatters and model math (all green)
- scripts/test.sh build+test loop driver
- docs/TESTING.md (5-gate process), docs/VALUE_PLAN.md (10x rubric)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

TopManagerTests/FormattingTests.swift

@@ -0,0 +1,114 @@
+import XCTest
+@testable import TopManager
+
+/// Baseline tests proving the test harness works and locking in the existing
+/// formatting / model-math behavior so later refactors can't silently break it.
+final class FormattingTests: XCTestCase {
+
+    // MARK: - Byte formatting
+
+    func testFormatBytesZero() {
+        // ByteCountFormatter renders 0 as "Zero KB"/"Zero bytes" depending on OS/locale.
+        let s = formatBytes(UInt64(0)).lowercased()
+        XCTAssertTrue(s.contains("zero") || s.contains("0"), "Unexpected zero rendering: \(s)")
+    }
+
+    func testFormatBytesGigabyteScale() {
+        // 2 GiB in binary style
+        let twoGiB = UInt64(2) * 1024 * 1024 * 1024
+        let s = formatBytes(twoGiB)
+        XCTAssertTrue(s.contains("GB"), "Expected GB unit, got \(s)")
+        XCTAssertTrue(s.contains("2"), "Expected value 2, got \(s)")
+    }
+
+    func testFormatBytesNegativeDoubleClampsToZero() {
+        // Double overload clamps negatives to 0 rather than trapping on UInt64(negative)
+        let s = formatBytes(Double(-500)).lowercased()
+        XCTAssertTrue(s.contains("zero") || s.contains("0"), "Unexpected clamp rendering: \(s)")
+    }
+
+    func testFormatBytesPerSecondBelowOne() {
+        XCTAssertEqual(formatBytesPerSecond(0.4), "0 B/s")
+    }
+
+    func testFormatBytesPerSecondSuffix() {
+        let s = formatBytesPerSecond(5 * 1024 * 1024) // 5 MiB/s
+        XCTAssertTrue(s.hasSuffix("/s"), "Expected /s suffix, got \(s)")
+        XCTAssertTrue(s.contains("MB"), "Expected MB unit, got \(s)")
+    }
+
+    // MARK: - Percentage
+
+    func testFormatPercentageDefaultDecimals() {
+        XCTAssertEqual(formatPercentage(12.345), "12.3%")
+    }
+
+    func testFormatPercentageCustomDecimals() {
+        XCTAssertEqual(formatPercentage(12.345, decimals: 2), "12.35%")
+    }
+
+    // MARK: - Uptime
+
+    func testFormatUptimeMinutesOnly() {
+        XCTAssertEqual(formatUptime(45 * 60), "45m")
+    }
+
+    func testFormatUptimeHoursAndMinutes() {
+        XCTAssertEqual(formatUptime(3 * 3600 + 12 * 60), "3h 12m")
+    }
+
+    func testFormatUptimeDays() {
+        XCTAssertEqual(formatUptime(2 * 86400 + 5 * 3600 + 9 * 60), "2d 5h 9m")
+    }
+
+    // MARK: - Model math
+
+    func testMemoryUsagePercentage() {
+        let mem = MemoryInfo(
+            totalMemory: 16_000_000_000,
+            usedMemory: 8_000_000_000,
+            freeMemory: 8_000_000_000,
+            activeMemory: 4_000_000_000,
+            inactiveMemory: 2_000_000_000,
+            wiredMemory: 2_000_000_000,
+            compressedMemory: 1_000_000_000,
+            cachedMemory: 1_000_000_000,
+            swapUsed: 0,
+            swapTotal: 0,
+            memoryPressure: .nominal
+        )
+        XCTAssertEqual(mem.usagePercentage, 50.0, accuracy: 0.001)
+        XCTAssertEqual(mem.appMemory, 6_000_000_000)
+    }
+
+    func testMemoryUsagePercentageZeroTotalIsSafe() {
+        let mem = MemoryInfo(
+            totalMemory: 0, usedMemory: 0, freeMemory: 0, activeMemory: 0,
+            inactiveMemory: 0, wiredMemory: 0, compressedMemory: 0, cachedMemory: 0,
+            swapUsed: 0, swapTotal: 0, memoryPressure: .unknown
+        )
+        XCTAssertEqual(mem.usagePercentage, 0)
+    }
+
+    func testVolumeUsagePercentageAndUsedSpace() {
+        let vol = VolumeInfo(
+            name: "Macintosh HD",
+            mountPoint: "/",
+            totalSpace: 1000,
+            freeSpace: 250,
+            fileSystem: "APFS",
+            isRemovable: false,
+            isInternal: true
+        )
+        XCTAssertEqual(vol.usedSpace, 750)
+        XCTAssertEqual(vol.usagePercentage, 75.0, accuracy: 0.001)
+    }
+
+    func testVolumeFreeGreaterThanTotalClampsUsedToZero() {
+        let vol = VolumeInfo(
+            name: "weird", mountPoint: "/x", totalSpace: 100, freeSpace: 200,
+            fileSystem: "APFS", isRemovable: false, isInternal: true
+        )
+        XCTAssertEqual(vol.usedSpace, 0)
+    }
+}