diff --git a/builder/dockerfile/support.go b/builder/dockerfile/support.go
index 38897b2cad..d2fdada874 100644
--- a/builder/dockerfile/support.go
+++ b/builder/dockerfile/support.go
@@ -2,6 +2,9 @@ package dockerfile
 
 import "strings"
 
+// handleJSONArgs parses command passed to CMD, ENTRYPOINT or RUN instruction in Dockerfile
+// for exec form it returns untouched args slice
+// for shell form it returns concatenated args as the first element of a slice
 func handleJSONArgs(args []string, attributes map[string]bool) []string {
 	if len(args) == 0 {
 		return []string{}
diff --git a/builder/dockerfile/support_test.go b/builder/dockerfile/support_test.go
new file mode 100644
index 0000000000..7cc6fe9dcb
--- /dev/null
+++ b/builder/dockerfile/support_test.go
@@ -0,0 +1,65 @@
+package dockerfile
+
+import "testing"
+
+type testCase struct {
+	name       string
+	args       []string
+	attributes map[string]bool
+	expected   []string
+}
+
+func initTestCases() []testCase {
+	testCases := []testCase{}
+
+	testCases = append(testCases, testCase{
+		name:       "empty args",
+		args:       []string{},
+		attributes: make(map[string]bool),
+		expected:   []string{},
+	})
+
+	jsonAttributes := make(map[string]bool)
+	jsonAttributes["json"] = true
+
+	testCases = append(testCases, testCase{
+		name:       "json attribute with one element",
+		args:       []string{"foo"},
+		attributes: jsonAttributes,
+		expected:   []string{"foo"},
+	})
+
+	testCases = append(testCases, testCase{
+		name:       "json attribute with two elements",
+		args:       []string{"foo", "bar"},
+		attributes: jsonAttributes,
+		expected:   []string{"foo", "bar"},
+	})
+
+	testCases = append(testCases, testCase{
+		name:       "no attributes",
+		args:       []string{"foo", "bar"},
+		attributes: nil,
+		expected:   []string{"foo bar"},
+	})
+
+	return testCases
+}
+
+func TestHandleJSONArgs(t *testing.T) {
+	testCases := initTestCases()
+
+	for _, test := range testCases {
+		arguments := handleJSONArgs(test.args, test.attributes)
+
+		if len(arguments) != len(test.expected) {
+			t.Fatalf("In test \"%s\": length of returned slice is incorrect. Expected: %d, got: %d", test.name, len(test.expected), len(arguments))
+		}
+
+		for i := range test.expected {
+			if arguments[i] != test.expected[i] {
+				t.Fatalf("In test \"%s\": element as position %d is incorrect. Expected: %s, got: %s", test.name, i, test.expected[i], arguments[i])
+			}
+		}
+	}
+}