ktesting: support verbosity changes at runtime

Being able to change the verbosity at runtime is useful. It is already
supported by the underlying code, ktesting and its Config struct just didn't
expose it.

ktesting/example_test.go

@@ -98,3 +98,26 @@ func ExampleNewLogger() {
 	// E...] I failed err="failure" what="something" data={field:1}
 	// I...] Logged at level 5.
 }
+
+func ExampleConfig_Verbosity() {
+	var buffer ktesting.BufferTL
+	config := ktesting.NewConfig(ktesting.Verbosity(1))
+	logger := ktesting.NewLogger(&buffer, config)
+
+	logger.Info("initial verbosity", "v", config.Verbosity().String())
+	logger.V(2).Info("now you don't see me")
+	if err := config.Verbosity().Set("2"); err != nil {
+		logger.Error(err, "setting verbosity to 2")
+	}
+	logger.V(2).Info("now you see me")
+	if err := config.Verbosity().Set("1"); err != nil {
+		logger.Error(err, "setting verbosity to 1")
+	}
+	logger.V(2).Info("now I'm gone again")
+
+	fmt.Print(headerRe.ReplaceAllString(buffer.String(), "${1}...] "))
+
+	// Output:
+	// I...] initial verbosity v="1"
+	// I...] now you see me
+}

ktesting/options.go

@@ -39,6 +39,20 @@ type Config struct {
 	co     configOptions
 }
 
+// Verbosity returns a value instance that can be used to query (via String) or
+// modify (via Set) the verbosity threshold. This is thread-safe and can be
+// done at runtime.
+func (c *Config) Verbosity() flag.Value {
+	return c.vstate.V()
+}
+
+// VModule returns a value instance that can be used to query (via String) or
+// modify (via Set) the vmodule settings. This is thread-safe and can be done
+// at runtime.
+func (c *Config) VModule() flag.Value {
+	return c.vstate.VModule()
+}
+
 // ConfigOption implements functional parameters for NewConfig.
 //
 // # Experimental