Add functions to make certain assertions

entrypoint/assertions.go

@@ -0,0 +1,41 @@
+package entrypoint
+
+import (
+	"fmt"
+	"github.com/urfave/cli"
+	"os"
+)
+
+type RequiredArgsError struct {
+	message string
+}
+
+func (err RequiredArgsError) Error() string {
+	return err.message
+}
+
+func NewRequiredArgsError(message string) error {
+	return &RequiredArgsError{message}
+}
+
+// StringFlagRequiredE checks if a required string flag is passed in on the CLI. This will return the set string, or an
+// error if the flag is not passed in.
+func StringFlagRequiredE(cliContext *cli.Context, flagName string) (string, error) {
+	value := cliContext.String(flagName)
+	if value == "" {
+		message := fmt.Sprintf("--%s is required", flagName)
+		return "", NewRequiredArgsError(message)
+	}
+	return value, nil
+}
+
+// EnvironmentVarRequiredE checks if a required environment variable is set. This will return the environment variable
+// value, or an error if the environment variable is not set.
+func EnvironmentVarRequiredE(varName string) (string, error) {
+	value := os.Getenv(varName)
+	if value == "" {
+		message := fmt.Sprintf("The environment variable %s is required to be set", varName)
+		return "", NewRequiredArgsError(message)
+	}
+	return value, nil
+}

entrypoint/assertions_test.go

@@ -0,0 +1,62 @@
+package entrypoint
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/urfave/cli"
+)
+
+func TestStringFlagRequiredOnMissingFlag(t *testing.T) {
+	t.Parallel()
+
+	app := createSampleAppWithRequiredFlag()
+	app.Action = func(cliContext *cli.Context) error {
+		value, err := StringFlagRequiredE(cliContext, "the-answer-to-all-problems")
+		assert.NotNil(t, err)
+		assert.IsType(t, &RequiredArgsError{}, err)
+		assert.Equal(t, value, "")
+		return nil
+	}
+	args := []string{"app"}
+	app.Run(args)
+}
+
+func TestStringFlagRequiredOnSetFlag(t *testing.T) {
+	t.Parallel()
+
+	app := createSampleAppWithRequiredFlag()
+	app.Action = func(cliContext *cli.Context) error {
+		value, err := StringFlagRequiredE(cliContext, "the-answer-to-all-problems")
+		assert.Nil(t, err)
+		assert.Equal(t, value, "42")
+		return nil
+	}
+	args := []string{"app", "--the-answer-to-all-problems", "42"}
+	app.Run(args)
+}
+
+func TestEnvironmentVarRequiredOnMissingEnvVar(t *testing.T) {
+	value, err := EnvironmentVarRequiredE("THE_ANSWER_TO_ALL_PROBLEMS")
+	assert.NotNil(t, err)
+	assert.IsType(t, &RequiredArgsError{}, err)
+	assert.Equal(t, value, "")
+}
+
+func TestEnvironmentVarRequiredOnSetEnvVar(t *testing.T) {
+	os.Setenv("THE_ANSWER_TO_ALL_PROBLEMS", "42")
+	value, err := EnvironmentVarRequiredE("THE_ANSWER_TO_ALL_PROBLEMS")
+	assert.Nil(t, err)
+	assert.Equal(t, value, "42")
+}
+
+func createSampleAppWithRequiredFlag() *cli.App {
+	app := cli.NewApp()
+	app.Flags = []cli.Flag{
+		cli.StringFlag{
+			Name: "the-answer-to-all-problems",
+		},
+	}
+	return app
+}