Fix test.assertraise treating return value of a call as its error

CHANGELOG.md

@@ -17,7 +17,8 @@
   - Fixed `pl.import_into` not importing some Penlight modules (#268).
   - Fixed version number stuck at 1.5.2 (#260).
   - Fixed `types.is_empty` returning `true` on tables containing `false` key (#267).
-  - Fixed `test.assertraise` throwing an error when passes an array with a function to call plus its arguments (#272).
+  - Fixed `test.assertraise` throwing an error when passed an array with a function to call plus its arguments (#272).
+  - Fixed `test.assertraise` not throwing an error when given function does not error but instead returns a string matching given error pattern.
   - Fixed placeholder expressions being evaluated with wrong precedence of binary and unary negation.
   - Fixed placeholder expressions being evaluated assuming wrong binary operator associativity (e.g. `_1-(_2+_3)` was evaluated as `(_1-_2)+_3`.
   - Fixed placeholder expressions being evaluated as if unary operators take precedence over power operator (e.g. `(-_1)^_2`) was evaluated as `-(_1^2)`).

lua/pl/test.lua

@@ -85,13 +85,13 @@ end
 -- @param e a string to match the error against
 -- @param where extra level offset
 function test.assertraise(fn,e,where)
-    local _, err
+    local ok, err
     if type(fn) == 'table' then
-        _, err = pcall(unpack(fn))
+        ok, err = pcall(unpack(fn))
     else
-        _, err = pcall(fn)
+        ok, err = pcall(fn)
     end
-    if not err or err:match(e)==nil then
+    if ok or err:match(e)==nil then
         complain (err,e,"these errors did not match",where)
     end
 end