Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: mertssmnoglu

docs/TESTING.md

@@ -173,7 +173,7 @@ For each combination the following steps run sequentially:
 | UsedBytes reflects the write   | `usedBytes >= 30 MB`                      |
 | UsedBytes within bounds        | `usedBytes <= totalBytes`                 |
 | UsagePercent in valid range    | `0 <= usagePct <= 1`                      |
-| UsagePercent is plausible      | `usagePct >= 0.20`                        |
+| UsagePercent is plausible      | `usagePct >= 0.15`                        |
 | Used + Free approximates Total | `abs(used + free - total) / total <= 10%` |
 
 ##### 7. Cleanup (deferred, runs in reverse order)

test/integration/disk_fs_test.go

@@ -103,6 +103,7 @@ func TestDiskFilesystemMetrics(t *testing.T) {
 				test.RequireCmd(t, "mkfs.btrfs")
 			case "zfs":
 				test.RequireCmd(t, "zpool")
+				test.RequireCmd(t, "zfs")
 			}
 
 			if tc.strategy == "lvm" {