Test if link metadata is generated correctly when no commands are passed

Signed-off-by: Aditya Sirish <aditya@saky.in>

in_toto/runlib.go

@@ -304,7 +304,7 @@ func InTotoRun(name string, runDir string, materialPaths []string, productPaths
 	}
 
 	// make sure that we only run RunCommand if cmdArgs is not nil or empty
-	var byProducts map[string]interface{}
+	byProducts := map[string]interface{}{}
 	if len(cmdArgs) != 0 {
 		byProducts, err = RunCommand(cmdArgs, runDir)
 		if err != nil {

in_toto/runlib_test.go

@@ -437,6 +437,30 @@ func TestInTotoRun(t *testing.T) {
 			}},
 		},
 		},
+		{[]string{"alice.pub"}, []string{"foo.tar.gz"}, []string{}, validKey, []string{"sha256"}, Metablock{
+			Signed: Link{
+				Name: linkName,
+				Type: "link",
+				Materials: map[string]interface{}{
+					"alice.pub": map[string]interface{}{
+						"sha256": "f051e8b561835b7b2aa7791db7bc72f2613411b0b7d428a0ac33d45b8c518039",
+					},
+				},
+				Products: map[string]interface{}{
+					"foo.tar.gz": map[string]interface{}{
+						"sha256": "52947cb78b91ad01fe81cd6aef42d1f6817e92b9e6936c1e5aabb7c98514f355",
+					},
+				},
+				ByProducts:  map[string]interface{}{},
+				Command:     []string{},
+				Environment: map[string]interface{}{},
+			},
+			Signatures: []Signature{{
+				KeyID: "be6371bc627318218191ce0780fd3183cce6c36da02938a477d2e4dfae1804a6",
+				Sig:   "f4a2d468965d595b4d29615fb2083ef7ac22a948e1530925612d73ba580ce9765d93db7b7ed1b9755d96f13a6a1e858c64693c2f7adcb311afb28cb57fbadc0c",
+			}},
+		},
+		},
 	}
 
 	for _, table := range tablesCorrect {