Track which phases causes each failure

Each merge test consists of three phases: merge, run, check output.
Until I added t/indent-block-py.t all failing tests did so during the
merge phase.  Now we have a test which causes Git to fail during the run
phase.

Eventually I'll visual this new data in a convenient format.  For now
it's available in the raw TAP output if anyone wants to see it.

Closes #11

lib/Test/Merges.pm

@@ -145,14 +145,24 @@ sub merge_ok {
         my $repo_name = "merge-$y-into-$x";
         clone $x, $repo_name;
         chdir $repo_name;
+
+        my @phases = qw( merge run output );
+        my $check  = sub {
+            my $phase = shift @phases;
+            pass("$phase ($y into $x)");
+        };
         try {
             perform_merge("../$y");
+            $check->();
             system("./run > obtained.txt");
+            $check->();
             system("diff -u expected.txt obtained.txt");
-            pass("merge $y into $x");
+            $check->();
+            pass("$y into $x");
         }
         catch {
-            fail("merge $y into $x");
+            fail($_) for @phases;
+            fail("$y into $x");
         };
         chdir '..';
     }

t/adjacent-changes.t

@@ -1,6 +1,6 @@
 use strict;
 use warnings;
-use Test::More tests => 2;
+use Test::More tests => 8;
 use Test::Merges;
 
 # Perform two changes on immediately adjacent lines.

t/dual-renames.t

@@ -1,6 +1,6 @@
 use strict;
 use warnings;
-use Test::More tests => 2;
+use Test::More tests => 8;
 use Test::Merges;
 
 # One branch renames a function.  The other branch renames that function's

t/eol-comment.t

@@ -1,6 +1,6 @@
 use strict;
 use warnings;
-use Test::More tests => 2;
+use Test::More tests => 8;
 use Test::Merges;
 
 # Add an end-of-line comment and change the same line

t/indent-block-py.t

@@ -1,6 +1,6 @@
 use strict;
 use warnings;
-use Test::More tests => 2;
+use Test::More tests => 8;
 use Test::Merges;
 
 # indent-block in Python

t/indent-block.t

@@ -1,6 +1,6 @@
 use strict;
 use warnings;
-use Test::More tests => 2;
+use Test::More tests => 8;
 use Test::Merges;
 
 # Modify and indent a block of code

t/move-modify.t

@@ -1,6 +1,6 @@
 use strict;
 use warnings;
-use Test::More tests => 2;
+use Test::More tests => 8;
 use Test::Merges;
 
 # One branch moves a file.  Another branch modifies the file.

t/nearby-changes.t

@@ -1,6 +1,6 @@
 use strict;
 use warnings;
-use Test::More tests => 2;
+use Test::More tests => 8;
 use Test::Merges;
 
 # Perform two changes on nearby lines

t/same-change.t

@@ -1,6 +1,6 @@
 use strict;
 use warnings;
-use Test::More tests => 2;
+use Test::More tests => 8;
 use Test::Merges;
 
 # Perform the exact same change in two separate branches.

t/trailing-whitespace.t

@@ -1,6 +1,6 @@
 use strict;
 use warnings;
-use Test::More tests => 2;
+use Test::More tests => 8;
 use Test::Merges;
 
 # Remove trailing whitespace on the same line as a meaningful change