cmd/go, testing: test names don't have to be alphanumeric

In func TestXxxx(*testing.T) the Xxxx can be anything that can appear
in an identifier, but can't start with a lowercase letter. Clarify the docs.

Fixes #23322

Change-Id: I5c297916981f7e3890ee955d12bc7422a75488e2
Reviewed-on: https://go-review.googlesource.com/86001
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/go/alldocs.go

@@ -1707,14 +1707,14 @@
 // The 'go test' command expects to find test, benchmark, and example functions
 // in the "*_test.go" files corresponding to the package under test.
 //
-// A test function is one named TestXXX (where XXX is any alphanumeric string
-// not starting with a lower case letter) and should have the signature,
+// A test function is one named TestXxx (where Xxx does not start with a
+// lower case letter) and should have the signature,
 //
-// 	func TestXXX(t *testing.T) { ... }
+// 	func TestXxx(t *testing.T) { ... }
 //
-// A benchmark function is one named BenchmarkXXX and should have the signature,
+// A benchmark function is one named BenchmarkXxx and should have the signature,
 //
-// 	func BenchmarkXXX(b *testing.B) { ... }
+// 	func BenchmarkXxx(b *testing.B) { ... }
 //
 // An example function is similar to a test function but, instead of using
 // *testing.T to report success or failure, prints output to os.Stdout.
@@ -1725,8 +1725,8 @@
 // comment is compiled but not executed. An example with no text after
 // "Output:" is compiled, executed, and expected to produce no output.
 //
-// Godoc displays the body of ExampleXXX to demonstrate the use
-// of the function, constant, or variable XXX. An example of a method M with
+// Godoc displays the body of ExampleXxx to demonstrate the use
+// of the function, constant, or variable Xxx. An example of a method M with
 // receiver type T or *T is named ExampleT_M. There may be multiple examples
 // for a given function, constant, or variable, distinguished by a trailing _xxx,
 // where xxx is a suffix not beginning with an upper case letter.

src/cmd/go/internal/test/test.go

@@ -406,14 +406,14 @@ var HelpTestfunc = &base.Command{
 The 'go test' command expects to find test, benchmark, and example functions
 in the "*_test.go" files corresponding to the package under test.
 
-A test function is one named TestXXX (where XXX is any alphanumeric string
-not starting with a lower case letter) and should have the signature,
+A test function is one named TestXxx (where Xxx does not start with a
+lower case letter) and should have the signature,
 
-	func TestXXX(t *testing.T) { ... }
+	func TestXxx(t *testing.T) { ... }
 
-A benchmark function is one named BenchmarkXXX and should have the signature,
+A benchmark function is one named BenchmarkXxx and should have the signature,
 
-	func BenchmarkXXX(b *testing.B) { ... }
+	func BenchmarkXxx(b *testing.B) { ... }
 
 An example function is similar to a test function but, instead of using
 *testing.T to report success or failure, prints output to os.Stdout.
@@ -424,8 +424,8 @@ comment, however the order of the lines is ignored. An example with no such
 comment is compiled but not executed. An example with no text after
 "Output:" is compiled, executed, and expected to produce no output.
 
-Godoc displays the body of ExampleXXX to demonstrate the use
-of the function, constant, or variable XXX. An example of a method M with
+Godoc displays the body of ExampleXxx to demonstrate the use
+of the function, constant, or variable Xxx. An example of a method M with
 receiver type T or *T is named ExampleT_M. There may be multiple examples
 for a given function, constant, or variable, distinguished by a trailing _xxx,
 where xxx is a suffix not beginning with an upper case letter.

src/testing/testing.go

@@ -6,8 +6,8 @@
 // It is intended to be used in concert with the ``go test'' command, which automates
 // execution of any function of the form
 //     func TestXxx(*testing.T)
-// where Xxx can be any alphanumeric string (but the first letter must not be in
-// [a-z]) and serves to identify the test routine.
+// where Xxx does not start with a lowercase letter. The function name
+// serves to identify the test routine.
 //
 // Within these functions, use the Error, Fail or related methods to signal failure.
 //