[Pkg-libvirt-commits] [libguestfs] 345/384: v2v: test-harness: Measure similarity between images when comparing screenshots.

[Hilko Bengen]

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bengen pushed a commit to branch experimental
in repository libguestfs.

commit a3beda8b77363e13f652104b06efaee33ecfe67c
Author: Richard W.M. Jones <rjones at redhat.com>
Date:   Wed Mar 11 15:02:58 2015 +0000

    v2v: test-harness: Measure similarity between images when comparing screenshots.
    
    Since wallclock time differs between boots, we cannot just compare two
    screenshots by checking if they are identical -- if the screenshot
    contains any time information, then that will be different, and it
    turns out that VMs print the current time at boot.
    
    Therefore parse out and use the "similarity" metric printed by the
    ImageMagick "compare" command when it compares the screenshots, and
    allow a small epsilon for the case where a few oixels are different.
---
 v2v/test-harness/v2v_test_harness.ml | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/v2v/test-harness/v2v_test_harness.ml b/v2v/test-harness/v2v_test_harness.ml
index cd08cd0..998903a 100644
--- a/v2v/test-harness/v2v_test_harness.ml
+++ b/v2v/test-harness/v2v_test_harness.ml
@@ -196,13 +196,29 @@ let run ~test ?input_disk ?input_xml ?(test_plan = default_plan) () =
 
     let display_matches_screenshot screenshot1 screenshot2 =
       let cmd =
-        sprintf "compare -metric MAE %s %s null:"
+        (* Grrr compare sends its normal output to stderr. *)
+        sprintf "compare -metric MAE %s %s null: 2>&1"
           (quote screenshot1) (quote screenshot2) in
       printf "%s\n%!" cmd;
-      let r = Sys.command cmd in
-      if r < 0 || r > 1 then
-        failwith "compare command failed";
-      r = 0
+      let chan = Unix.open_process_in cmd in
+      let lines = ref [] in
+      (try while true do lines := input_line chan :: !lines done
+       with End_of_file -> ());
+      let lines = List.rev !lines in
+      let stat = Unix.close_process_in chan in
+      let similarity =
+        match stat with
+        | Unix.WEXITED 0 -> 0.0 (* exact match *)
+        | Unix.WEXITED 1 ->
+          Scanf.sscanf (List.hd lines) "%f" (fun f -> f)
+        | Unix.WEXITED i ->
+          failwithf "external command '%s' exited with error %d" cmd i
+        | Unix.WSIGNALED i ->
+          failwithf "external command '%s' killed by signal %d" cmd i
+        | Unix.WSTOPPED i ->
+          failwithf "external command '%s' stopped by signal %d" cmd i in
+      printf "%s %s have similarity %f\n" screenshot1 screenshot2 similarity;
+      similarity <= 60.0
     in
 
     let dom_is_alive () =

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