Adding test coverage for new error catching

Author: anujthak

gap/io.gi

@@ -2223,12 +2223,21 @@ InstallMethod(Graph6String, "for a digraph by out-neighbours",
 function(D)
   local list, adj, n, lenlist, tablen, blist, i, j, pos, block;
   if IsMultiDigraph(D) then
-    ErrorNoReturn("the argument <D> must not have multiple edges; consider encoding in Disparse6 or Digraph6");
-elif not IsSymmetricDigraph(D) then
-    ErrorNoReturn("the argument <D> must be a symmetric digraph; consider encoding in Sparse6 or Disparse6");
-elif DigraphHasLoops(D) then
-    ErrorNoReturn("the argument <D> must not have loops; consider encoding in Sparse6 or Disparse6");
-fi;
+    ErrorNoReturn(
+      "the argument <D> must not have multiple edges; ",
+      "consider encoding in Disparse6 or Digraph6"
+    );
+  elif not IsSymmetricDigraph(D) then
+    ErrorNoReturn(
+      "the argument <D> must be a symmetric digraph; ",
+      "consider encoding in Sparse6 or Disparse6"
+    );
+  elif DigraphHasLoops(D) then
+    ErrorNoReturn(
+      "the argument <D> must not have loops; ",
+      "consider encoding in Sparse6 or Disparse6"
+    );
+  fi;
 
   list := [];
   adj := OutNeighbours(D);
@@ -2351,9 +2360,15 @@ function(D)
 
   if not IsSymmetricDigraph(D) then
     if IsMultiDigraph(D) then
-        ErrorNoReturn("the argument <D> must be a symmetric digraph consider encoding in Disparse6,");
+      ErrorNoReturn(
+        "the argument <D> must be a symmetric digraph; ",
+        "consider encoding in Disparse6"
+      );
     else
-        ErrorNoReturn("the argument <D> must be a symmetric digraph consider encoding in Digraph6 or Disparse6,");
+      ErrorNoReturn(
+        "the argument <D> must be a symmetric digraph; ",
+        "consider encoding in Digraph6 or Disparse6"
+      );
     fi;
   fi;
 

tst/standard/io.tst

@@ -546,8 +546,8 @@ Error, the 2nd argument <s> is not a valid disparse6 string,
 
 #  Special format characters
 gap> Sparse6String(ChainDigraph(3));
-Error, the argument <D> must be a symmetric digraph consider encoding in Digra\
-ph6 or Disparse6,
+Error, the argument <D> must be a symmetric digraph; consider encoding in Digr\
+aph6 or Disparse6
 gap> Sparse6String(CompleteDigraph(1));
 ":@"
 gap> gr := Digraph([[1], []]);;
@@ -560,6 +560,24 @@ gap> DigraphFromSparse6String(":TdBkJ`Kq?x");
 gap> Sparse6String(last);
 ":TdBkJ`Kq?"
 
+# Multiple Edges Digraph6
+gap> gr := Digraph([[1,1], [2]]);;
+gap> Digraph6String(gr);
+Error, the argument <D> must not have multiple edges consider encoding in Spar\
+se6 or Disparse6, 
+
+# Non-symmetric Digraph in Sparse6
+gap> gr := Digraph([[2], []]);;
+gap> Sparse6String(gr);
+Error, the argument <D> must be a symmetric digraph; consider encoding in Digr\
+aph6 or Disparse6
+
+# Digraph with loops in Sparse6
+gap> gr := Digraph([[1], [2]]);;
+gap> Graph6String(gr);
+Error, the argument <D> must not have loops; consider encoding in Sparse6 or D\
+isparse6
+
 #  DigraphPlainTextLineDecoder: bad input
 gap> DigraphPlainTextLineDecoder(" ", "  ", 1, ".");
 Error, no method found! For debugging hints type ?Recovery from NoMethodFound