completion: add test for EnvVarNames

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

cli/command/completion/functions_test.go

@@ -1,13 +1,28 @@
 package completion
 
 import (
+	"sort"
 	"testing"
 
 	"github.com/spf13/cobra"
 	"gotest.tools/v3/assert"
 	is "gotest.tools/v3/assert/cmp"
+	"gotest.tools/v3/env"
 )
 
+func TestCompleteEnvVarNames(t *testing.T) {
+	env.PatchAll(t, map[string]string{
+		"ENV_A": "hello-a",
+		"ENV_B": "hello-b",
+	})
+	values, directives := EnvVarNames(nil, nil, "")
+	assert.Check(t, is.Equal(directives&cobra.ShellCompDirectiveNoFileComp, cobra.ShellCompDirectiveNoFileComp), "Should not perform file completion")
+
+	sort.Strings(values)
+	expected := []string{"ENV_A", "ENV_B"}
+	assert.Check(t, is.DeepEqual(values, expected))
+}
+
 func TestCompletePlatforms(t *testing.T) {
 	values, directives := Platforms(nil, nil, "")
 	assert.Check(t, is.Equal(directives&cobra.ShellCompDirectiveNoFileComp, cobra.ShellCompDirectiveNoFileComp), "Should not perform file completion")