diff --git a/src/libvterm/t/02parser.test b/src/libvterm/t/02parser.test
index 66d487d..4a4a65b 100644
--- a/src/libvterm/t/02parser.test
+++ b/src/libvterm/t/02parser.test
@@ -132,15 +132,23 @@
 
 !OSC BEL
 PUSH "\e]1;Hello\x07"
-  osc "1;Hello"
+  osc [1 "Hello"]
 
 !OSC ST (7bit)
 PUSH "\e]1;Hello\e\\"
-  osc "1;Hello"
+  osc [1 "Hello"]
 
 !OSC ST (8bit)
 PUSH "\x{9d}1;Hello\x9c"
-  osc "1;Hello"
+  osc [1 "Hello"]
+
+!OSC in parts
+PUSH "\e]52;abc"
+  osc [52 "abc"
+PUSH "def"
+  osc "def"
+PUSH "ghi\e\\"
+  osc "ghi"]
 
 !Escape cancels OSC, starts Escape
 PUSH "\e]Something\e9"
@@ -152,20 +160,21 @@
 
 !C0 in OSC interrupts and continues
 PUSH "\e]2;\nBye\x07"
+  osc [2 ""
   control 10
-  osc "2;Bye"
+  osc "Bye"]
 
 !DCS BEL
 PUSH "\ePHello\x07"
-  dcs "Hello"
+  dcs ["Hello"]
 
 !DCS ST (7bit)
 PUSH "\ePHello\e\\"
-  dcs "Hello"
+  dcs ["Hello"]
 
 !DCS ST (8bit)
 PUSH "\x{90}Hello\x9c"
-  dcs "Hello"
+  dcs ["Hello"]
 
 !Escape cancels DCS, starts Escape
 PUSH "\ePSomething\e9"
@@ -177,8 +186,9 @@
 
 !C0 in OSC interrupts and continues
 PUSH "\ePBy\ne\x07"
+  dcs ["By"
   control 10
-  dcs "Bye"
+  dcs "e"]
 
 !NUL ignored
 PUSH "\x{00}"
diff --git a/src/libvterm/t/18state_termprops.test b/src/libvterm/t/18state_termprops.test
index 9e6928a..83c333f 100644
--- a/src/libvterm/t/18state_termprops.test
+++ b/src/libvterm/t/18state_termprops.test
@@ -33,4 +33,10 @@
 
 !Title
 PUSH "\e]2;Here is my title\a"
-  settermprop 4 "Here is my title"
+  settermprop 4 ["Here is my title"]
+
+!Title split write
+PUSH "\e]2;Here is"
+  settermprop 4 ["Here is"
+PUSH " another title\a"
+  settermprop 4 " another title"]
diff --git a/src/libvterm/t/29state_fallback.test b/src/libvterm/t/29state_fallback.test
index adf1c23..7995dd1 100644
--- a/src/libvterm/t/29state_fallback.test
+++ b/src/libvterm/t/29state_fallback.test
@@ -12,8 +12,8 @@
 
 !Unrecognised OSC
 PUSH "\e]27;Something\e\\"
-  osc "27;Something"
+  osc [27 "Something"]
 
 !Unrecognised DCS
 PUSH "\ePz123\e\\"
-  dcs "z123"
+  dcs ["z123"]
diff --git a/src/libvterm/t/68screen_termprops.test b/src/libvterm/t/68screen_termprops.test
index adf7ec2..bba6660 100644
--- a/src/libvterm/t/68screen_termprops.test
+++ b/src/libvterm/t/68screen_termprops.test
@@ -14,4 +14,4 @@
 
 !Title
 PUSH "\e]2;Here is my title\a"
-  settermprop 4 "Here is my title"
+  settermprop 4 ["Here is my title"]
diff --git a/src/libvterm/t/harness.c b/src/libvterm/t/harness.c
index 289d829..92882fd 100644
--- a/src/libvterm/t/harness.c
+++ b/src/libvterm/t/harness.c
@@ -153,21 +153,44 @@
   return 1;
 }
 
-static int parser_osc(const char *command, size_t cmdlen, void *user UNUSED)
+static int parser_osc(int command, VTermStringFragment frag, void *user UNUSED)
 {
 
   printf("osc ");
-  printhex(command, cmdlen);
+
+  if(frag.initial) {
+    if(command == -1)
+      printf("[");
+    else
+      printf("[%d;", command);
+  }
+
+  printhex(frag.str, frag.len);
+
+  if(frag.final)
+    printf("]");
+
   printf("\n");
 
   return 1;
 }
 
-static int parser_dcs(const char *command, size_t cmdlen, void *user UNUSED)
+static int parser_dcs(const char *command, size_t commandlen, VTermStringFragment frag, void *user UNUSED)
 {
-
   printf("dcs ");
-  printhex(command, cmdlen);
+
+  if(frag.initial) {
+    size_t i;
+    printf("[");
+    for(i = 0; i < commandlen; i++)
+      printf("%02x", command[i]);
+  }
+
+  printhex(frag.str, frag.len);
+
+  if(frag.final)
+    printf("]");
+
   printf("\n");
 
   return 1;
@@ -239,7 +262,8 @@
     printf("settermprop %d %d\n", prop, val->number);
     return 1;
   case VTERM_VALUETYPE_STRING:
-    printf("settermprop %d \"%s\"\n", prop, val->string);
+    printf("settermprop %d %s\"%.*s\"%s\n", prop,
+        val->string.initial ? "[" : "", val->string.len, val->string.str, val->string.final ? "]" : "");
     return 1;
   case VTERM_VALUETYPE_COLOR:
     printf("settermprop %d rgb(%d,%d,%d)\n", prop, val->color.red, val->color.green, val->color.blue);
@@ -262,7 +286,7 @@
     return 1;
 
   printf("putglyph ");
-  for(i = 0; info->chars[i]; i++)
+  for(i = 0; i < VTERM_MAX_CHARS_PER_CELL && info->chars[i]; i++)
     printf(i ? ",%x" : "%x", info->chars[i]);
   printf(" %d %d,%d", info->width, pos.row, pos.col);
   if(info->protected_cell)
diff --git a/src/libvterm/t/run-test.pl b/src/libvterm/t/run-test.pl
index 5f3c78d..9f48c5c 100644
--- a/src/libvterm/t/run-test.pl
+++ b/src/libvterm/t/run-test.pl
@@ -11,7 +11,8 @@
 my $EXECUTABLE = "t/.libs/harness";
 GetOptions(
    'valgrind|v+' => \$VALGRIND,
-   'executable|e=s' => \$EXECUTABLE
+   'executable|e=s' => \$EXECUTABLE,
+   'fail-early|F' => \(my $FAIL_EARLY),
 ) or exit 1;
 
 my ( $hin, $hout, $hpid );
@@ -65,6 +66,7 @@
    }
 
    $exitcode = 1 if $fail_printed;
+   exit $exitcode if $exitcode and $FAIL_EARLY;
 }
 
 sub do_line
@@ -105,8 +107,15 @@
       elsif( $line =~ m/^csi (\S+) (.*)$/ ) {
          $line = sprintf "csi %02x %s", eval($1), $2; # TODO
       }
-      elsif( $line =~ m/^(escape|osc|dcs) (.*)$/ ) {
-         $line = "$1 " . join "", map sprintf("%02x", $_), unpack "C*", eval($2);
+      elsif( $line =~ m/^(osc) (\[\d+)? *(.*?)(\]?)$/ ) {
+         my ( $cmd, $initial, $data, $final ) = ( $1, $2, $3, $4 );
+         $initial //= "";
+         $initial .= ";" if $initial =~ m/\d+/;
+
+         $line = "$cmd $initial" . join( "", map sprintf("%02x", $_), unpack "C*", eval($data) ) . "$final";
+      }
+      elsif( $line =~ m/^(escape|dcs) (\[?)(.*?)(\]?)$/ ) {
+         $line = "$1 $2" . join( "", map sprintf("%02x", $_), unpack "C*", eval($3) ) . "$4";
       }
       elsif( $line =~ m/^putglyph (\S+) (.*)$/ ) {
          $line = "putglyph " . join( ",", map sprintf("%x", $_), eval($1) ) . " $2";
@@ -139,6 +148,7 @@
                "# Expected: $want\n" .
                "# Actual:   $response\n";
          $exitcode = 1;
+         exit $exitcode if $exitcode and $FAIL_EARLY;
       }
    }
    # Assertions start with '?'
@@ -162,6 +172,7 @@
                "# Expected: $expectation\n" .
                "# Actual:   $response\n";
          $exitcode = 1;
+         exit $exitcode if $exitcode and $FAIL_EARLY;
       }
    }
    # Test controls start with '$'