Make describe output for envvars deterministic

As `describe` uses a map to store the env var kv pairs its output varies
in its order.  This is undesirable.

This change introduces a means by which env var output ordering is
predictable.

Signed-off-by: Richard Gee <richard@technologee.co.uk>

commands/describe.go

@@ -9,6 +9,7 @@ import (
 	"io"
 	"os"
 	"reflect"
+	"sort"
 	"strconv"
 	"strings"
 	"text/tabwriter"
@@ -225,6 +226,15 @@ func printMap(w io.Writer, name string, m map[string]string, verbose bool) {
 	}
 
 	fmt.Fprintf(w, "%s:\n", name)
+
+	if name == "Environment" {
+		orderedKeys := generateMapOrder(m)
+		for _, keyName := range orderedKeys {
+			fmt.Fprintln(w, "\t "+keyName+": "+m[keyName])
+		}
+		return
+	}
+
 	for key, value := range m {
 		fmt.Fprintln(w, "\t "+key+": "+value)
 	}
@@ -286,3 +296,16 @@ func isEmpty(a interface{}) bool {
 	}
 	return false
 }
+
+func generateMapOrder(m map[string]string) []string {
+
+	var keyNames []string
+
+	for keyName := range m {
+		keyNames = append(keyNames, keyName)
+	}
+
+	sort.Strings(keyNames)
+
+	return keyNames
+}

commands/describe_test.go

@@ -148,3 +148,56 @@ func TestDescribeOuput(t *testing.T) {
 		})
 	}
 }
+
+func TestGenerateMapOrder(t *testing.T) {
+	var generateMapOrderTestcases = []struct {
+		Name       string
+		Input      map[string]string
+		Output     []string
+		expectFail bool
+	}{
+		{
+			Name: "One item",
+			Input: map[string]string{
+				"AAA": "aaa",
+			},
+			Output:     []string{"AAA"},
+			expectFail: false,
+		},
+		{
+			Name: "Multiple items",
+			Input: map[string]string{
+				"AAA": "aaa",
+				"BBB": "bbb",
+				"CCC": "ccc",
+				"DDD": "ddd",
+			},
+			Output:     []string{"AAA", "BBB", "CCC", "DDD"},
+			expectFail: false,
+		},
+		{
+			Name: "Multiple items but use a value",
+			Input: map[string]string{
+				"AAA": "aaa",
+				"BBB": "bbb",
+				"CCC": "ccc",
+				"DDD": "ddd",
+			},
+			Output:     []string{"AAA", "BBB", "CCC", "ddd"},
+			expectFail: true,
+		},
+	}
+	for _, testcase := range generateMapOrderTestcases {
+		orderedSlice := generateMapOrder(testcase.Input)
+		if len(orderedSlice) != len(testcase.Output) {
+			t.Errorf("Slice sizes do not match: %s", testcase.Name)
+			t.Fail()
+		}
+		for i, v := range testcase.Output {
+			if v != orderedSlice[i] && !testcase.expectFail {
+				t.Errorf("Exected %s got %s: %s", v, orderedSlice[i], testcase.Name)
+				t.Fail()
+			}
+		}
+	}
+}