From a802d137cdb74d36a895f2c60333965c25ab2749 Mon Sep 17 00:00:00 2001
From: Arik Kfir <arik@kfirs.com>
Date: Mon, 17 Jun 2024 16:18:21 +0300
Subject: [PATCH] feat: support slowing down tests to enable debugging
 consequences

This change introduces a supported environment variable called
`JUSTEST_SLOW_FACTOR` which, when set to an integer value, will cause
Justest to multiple durations passed to the `For(...)` and `Within(...)`
methods with its value. This will cause these duration to be longer,
thus allowing the developer to investigate or debug side consequences of
such tests - like logging into clusters and checking the effects of
end-to-end tests, inspecting file-systems, etc.
---
 asserter.go  |  6 ++++++
 util.go      | 21 +++++++++++++++++++++
 util_test.go | 14 ++++++++++++++
 3 files changed, 41 insertions(+)
 create mode 100644 util.go
 create mode 100644 util_test.go

diff --git a/asserter.go b/asserter.go
index c9cc2ea..fbcff26 100644
--- a/asserter.go
+++ b/asserter.go
@@ -10,6 +10,8 @@ import (
 	"github.com/arikkfir/justest/internal"
 )
 
+const SlowFactorEnvVarName = "JUSTEST_SLOW_FACTOR"
+
 //go:noinline
 func With(t T) VerifierAndEnsurer {
 	if t == nil {
@@ -109,6 +111,8 @@ func (a *assertion) OrFail() {
 //go:noinline
 func (a *assertion) For(duration time.Duration, interval time.Duration) {
 	GetHelper(a.t).Helper()
+	duration = transformDurationIfNecessary(a.t, duration)
+
 	if a.evaluated {
 		panic("assertion already evaluated")
 	} else {
@@ -194,6 +198,8 @@ func (a *assertion) For(duration time.Duration, interval time.Duration) {
 //go:noinline
 func (a *assertion) Within(duration time.Duration, interval time.Duration) {
 	GetHelper(a.t).Helper()
+	duration = transformDurationIfNecessary(a.t, duration)
+
 	if a.evaluated {
 		panic("assertion already evaluated")
 	} else {
diff --git a/util.go b/util.go
new file mode 100644
index 0000000..1ede2fd
--- /dev/null
+++ b/util.go
@@ -0,0 +1,21 @@
+package justest
+
+import (
+	"os"
+	"strconv"
+	"time"
+)
+
+func transformDurationIfNecessary(t T, d time.Duration) time.Duration {
+	if v, found := os.LookupEnv(SlowFactorEnvVarName); found {
+		if factor, err := strconv.ParseInt(v, 0, 0); err != nil {
+			t.Logf("Ignoring value of '%s' environment variable: %+v", SlowFactorEnvVarName, err)
+			return d
+		} else {
+			oldSeconds := int64(d.Seconds())
+			newSeconds := oldSeconds * factor
+			return time.Duration(newSeconds) * time.Second
+		}
+	}
+	return d
+}
diff --git a/util_test.go b/util_test.go
new file mode 100644
index 0000000..2cd47ff
--- /dev/null
+++ b/util_test.go
@@ -0,0 +1,14 @@
+package justest
+
+import (
+	"testing"
+	"time"
+)
+
+func TestTransformDurationIfNecessary(t *testing.T) {
+	With(t).Verify(transformDurationIfNecessary(t, 5*time.Second)).Will(EqualTo(5 * time.Second)).OrFail()
+	t.Setenv(SlowFactorEnvVarName, "2")
+	With(t).Verify(transformDurationIfNecessary(t, 5*time.Second)).Will(EqualTo(10 * time.Second)).OrFail()
+	t.Setenv(SlowFactorEnvVarName, "3")
+	With(t).Verify(transformDurationIfNecessary(t, 5*time.Second)).Will(EqualTo(15 * time.Second)).OrFail()
+}