diff --git a/src/steps/partition.rs b/src/steps/partition.rs
index 6e2dd43..a061c44 100644
--- a/src/steps/partition.rs
+++ b/src/steps/partition.rs
@@ -1650,3 +1650,188 @@ fn format_number_thousands(n: u64) -> String {
     }
     result
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::installer::{LogicalVolume, PartitionTableType};
+
+    fn disk(name: &str, size_gb: u64) -> DiskInfo {
+        DiskInfo {
+            name: name.to_string(),
+            vendor: "ATA".to_string(),
+            model: "VBOX HARDDISK".to_string(),
+            drive_type: "HDD".to_string(),
+            size_gb,
+            size_bytes: size_gb * 1_073_741_824,
+        }
+    }
+
+    fn part(device: &str, size_mb: u64, fstype: FsType, mountpoint: &str) -> CustomPartition {
+        CustomPartition {
+            device: device.to_string(),
+            size_mb,
+            fstype,
+            mountpoint: mountpoint.to_string(),
+            encrypt: false,
+            luks_password: String::new(),
+            luks_name: String::new(),
+            skip_format: false,
+        }
+    }
+
+    fn step(uefi: bool) -> PartitionStep {
+        PartitionStep {
+            scanned: true,
+            is_uefi: uefi,
+            manual: ManualState::default(),
+            show_luks_password: false,
+            selected_disk_size_mb: None,
+        }
+    }
+
+    // ── make_plan ────────────────────────────────────────────
+
+    #[test]
+    fn plan_rejects_small_disk() {
+        let d = disk("/dev/sdb", 9);
+        assert!(make_plan(&d, true).is_none());
+        assert!(make_plan(&d, false).is_none());
+    }
+
+    #[test]
+    fn plan_uefi_large_disk() {
+        let d = disk("/dev/sda", 100);
+        let plan = make_plan(&d, true).expect("100GB disk için plan oluşmalı");
+        assert_eq!(plan.disk, "/dev/sda");
+        assert_eq!(plan.table_type, PartitionTableType::Gpt);
+        assert!(plan.efi_mb > 0, "UEFI planında EFI bölümü olmalı");
+        // EFI + swap + root, overhead payı düşülmüş disk boyutunu aşmamalı
+        assert!(plan.efi_mb + plan.swap_mb + plan.root_mb <= 100 * 1024);
+    }
+
+    #[test]
+    fn plan_bios_large_disk() {
+        let d = disk("/dev/sda", 100);
+        let plan = make_plan(&d, false).expect("100GB disk için plan oluşmalı");
+        assert_eq!(plan.table_type, PartitionTableType::Mbr);
+        assert_eq!(plan.efi_mb, 0, "BIOS modunda EFI bölümü olmamalı");
+    }
+
+    // ── validate_manual ───────────────────────────────────────
+
+    #[test]
+    fn manual_empty_plan_fails() {
+        assert!(validate_manual(&[], &[], true).is_some());
+        assert!(validate_manual(&[], &[], false).is_some());
+    }
+
+    #[test]
+    fn manual_root_only_ok_on_bios() {
+        let parts = vec![part("/dev/sda1", 20_000, FsType::Ext4, "/")];
+        assert!(validate_manual(&parts, &[], false).is_none());
+    }
+
+    #[test]
+    fn manual_uefi_requires_efi_part() {
+        let parts = vec![part("/dev/sda1", 20_000, FsType::Ext4, "/")];
+        assert!(
+            validate_manual(&parts, &[], true).is_some(),
+            "UEFI modunda EFI bölümü zorunlu"
+        );
+
+        let with_efi = vec![
+            part("/dev/sda1", 300, FsType::Fat32, "/boot/efi"),
+            part("/dev/sda2", 20_000, FsType::Ext4, "/"),
+        ];
+        assert!(validate_manual(&with_efi, &[], true).is_none());
+    }
+
+    #[test]
+    fn manual_root_can_come_from_lv() {
+        let parts = vec![part("/dev/sda1", 20_000, FsType::Lvm, "")];
+        let lvs = vec![LogicalVolume {
+            name: "root".to_string(),
+            vg_name: "vg0".to_string(),
+            size_mb: 10_000,
+            fstype: FsType::Ext4,
+            mountpoint: "/".to_string(),
+        }];
+        assert!(validate_manual(&parts, &lvs, false).is_none());
+    }
+
+    // ── InstallerStep arayüzü ─────────────────────────────────
+
+    #[test]
+    fn auto_mode_complete_only_with_plan() {
+        let st = step(true);
+        let mut state = crate::installer::GlobalState::default();
+        state.erase_disk = true;
+
+        assert!(!st.is_complete(&state), "plan yokken tamamlanmamalı");
+        state.partition_plan = make_plan(&disk("/dev/sda", 100), true);
+        assert!(st.is_complete(&state), "plan varken tamamlanmalı");
+    }
+
+    #[test]
+    fn manual_mode_complete_with_valid_partitions() {
+        let st = step(true);
+        let mut state = crate::installer::GlobalState::default();
+        state.erase_disk = false;
+
+        assert!(!st.is_complete(&state), "bölüm yokken tamamlanmamalı");
+
+        // Kök var ama EFI yok → tamamlanmamalı
+        state.custom_partitions.push(part("/dev/sda1", 20_000, FsType::Ext4, "/"));
+        assert!(!st.is_complete(&state), "eksik EFI bölümü ile tamamlanmamalı");
+
+        // Geçerli düzen → tamamlanmalı
+        state.custom_partitions.push(part("/dev/sda1", 300, FsType::Fat32, "/boot/efi"));
+        assert!(st.is_complete(&state), "geçerli düzen ile tamamlanmalı");
+    }
+
+    // ── format_number_thousands ───────────────────────────────
+
+    #[test]
+    fn formats_thousands() {
+        assert_eq!(format_number_thousands(0), "0");
+        assert_eq!(format_number_thousands(999), "999");
+        assert_eq!(format_number_thousands(1000), "1.000");
+        assert_eq!(format_number_thousands(7000000), "7.000.000");
+    }
+
+    // ── detect_drive_type ─────────────────────────────────────
+
+    #[test]
+    fn drive_type_by_name() {
+        assert_eq!(detect_drive_type("nvme0n1"), "NVMe SSD");
+        assert_eq!(detect_drive_type("mmcblk0"), "MMC/SD");
+        assert_eq!(detect_drive_type("nonexistent99"), "HDD");
+    }
+
+    // ── lsblk / sysfs okumaları (canlı sistem) ────────────────
+
+    #[test]
+    fn read_existing_partitions_never_panics() {
+        // Var olmayan disk → boş liste, çökmemeli
+        assert!(read_existing_partitions("/dev/does-not-exist").is_empty());
+
+        // Var olan disklerde dönen bölümler /dev/ ön ekli olmalı
+        for d in list_block_devices().iter().take(1) {
+            for p in read_existing_partitions(&d.name) {
+                assert!(p.device.starts_with("/dev/"));
+            }
+        }
+    }
+
+    #[test]
+    fn list_block_devices_scrubs_loop_ram() {
+        for d in list_block_devices() {
+            let base = d.name.trim_start_matches("/dev/");
+            assert!(!base.starts_with("loop"));
+            assert!(!base.starts_with("ram"));
+            assert!(!base.starts_with("sr"));
+            assert!(!base.starts_with("zram"));
+        }
+    }
+}