Fix explicit description behavior, add documentation to docstring

stdlib/Test/src/Test.jl

@@ -1225,6 +1225,7 @@ end
     @testset [CustomTestSet] [option=val  ...] ["description"] begin ... end
     @testset [CustomTestSet] [option=val  ...] ["description \$v"] for v in (...) ... end
     @testset [CustomTestSet] [option=val  ...] ["description \$v, \$w"] for v in (...), w in (...) ... end
+    @testset [CustomTestSet] [option=val  ...] ["description \$v, \$w"] foo()
 
 Starts a new test set, or multiple test sets if a `for` loop is provided.
 
@@ -1241,6 +1242,7 @@ nested testsets is shown even when they all pass (the default is `false`).
 
 The description string accepts interpolation from the loop indices.
 If no description is provided, one is constructed based on the variables.
+If a function call is provided, its name will be used. Explicit description strings override this behavior.
 
 By default the `@testset` macro will return the testset object itself, though
 this behavior can be customized in other testset types. If a `for` loop is used
@@ -1293,10 +1295,11 @@ Generate the code for a `@testset` with a function call or `begin`/`end` argumen
 function testset_beginend_call(args, tests, source)
     desc, testsettype, options = parse_testset_args(args[1:end-1])
     if desc === nothing
-        desc = "test set"
-    end
-    if tests.head === :call
-        desc = string(tests.args[1]) # use the function name as test name
+        if tests.head === :call
+            desc = string(tests.args[1]) # use the function name as test name
+        else
+            desc = "test set"
+        end
     end
     # If we're at the top level we'll default to DefaultTestSet. Otherwise
     # default to the type of the parent testset

stdlib/Test/test/runtests.jl

@@ -1250,8 +1250,10 @@ let
         end
     end
     tret = @testset h(1)
+    tdesc = @testset "description" h(1)
     @testset "Function calls" begin
         @test tret.description == "h"
+        @test tdesc.description == "description"
         @test length(tret.results) == 5
         @test tret.results[1].description == "f"
         @test tret.results[2].description == "success"