Fixes #2889. Merges *tostring tests in tests/system.

lib/system.nim

@@ -2235,7 +2235,9 @@ proc `$`*[T: tuple|object](x: T): string =
     firstElement = false
   result.add(")")
 
-proc collectionToString[T](x: T, b, e: string): string =
+proc collectionToString[T: set | seq](x: T, b, e: string): string =
+  when x is seq:
+    if x.isNil: return "nil"
   result = b
   var firstElement = true
   for value in items(x):

tests/system/tfloatToString.nim

@@ -1,22 +0,0 @@
-discard """
-  output:'''2.3242
-2.982
-123912.1
-123912.1823
-5.0
-1e+100
-inf
--inf
-nan
-'''
-"""
-
-echo($(2.3242))
-echo($(2.982))
-echo($(123912.1))
-echo($(123912.1823))
-echo($(5.0))
-echo($(1e100))
-echo($(1e1000000))
-echo($(-1e1000000))
-echo($(0.0/0.0))

tests/system/toString.nim

@@ -1,9 +1,42 @@
 discard """
   output:'''@[23, 45]
-@[, foo, bar]'''
+@[, foo, bar]
+{a, b, c}
+2.3242
+2.982
+123912.1
+123912.1823
+5.0
+1e+100
+inf
+-inf
+nan
+nil
+nil'''
 """
 
 echo($(@[23, 45]))
 echo($(@["", "foo", "bar"]))
 #echo($(["", "foo", "bar"]))
 #echo($([23, 45]))
+
+# bug #2395
+
+let alphaSet: set[char] = {'a'..'c'}
+echo alphaSet
+
+echo($(2.3242))
+echo($(2.982))
+echo($(123912.1))
+echo($(123912.1823))
+echo($(5.0))
+echo($(1e100))
+echo($(1e1000000))
+echo($(-1e1000000))
+echo($(0.0/0.0))
+
+# nil tests
+var x: seq[string]
+var y: string
+echo(x)
+echo(y)

tests/system/tsettostring.nim

@@ -1,8 +0,0 @@
-discard """
-  output: "{a, b, c}"
-"""
-
-# bug #2395
-
-let alphaSet: set[char] = {'a'..'c'}
-echo alphaSet