Add configurable scalaCheckInitialSeed

scalameta · Apr 1, 2020 · 7857d0e · 7857d0e
1 parent 1abd10d
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diff --git a/docs/integrations/scalacheck.md b/docs/integrations/scalacheck.md
@@ -124,21 +124,26 @@ non-deterministically. This can happen due to the randomness of the input values
 for each test run.
 
 When this happens, you can deterministally reproduce a property failure by using
-its seed. MUnit prints the property seed whenever a failure occurs in the form
-of:
+its seed. Whenever a failure occurs, MUnit prints the offending seed along with
+a suggestion on how to reproduce it:
 
 ```
 Failing seed: CTH6hXj8ViScMmsO78-k4_RytXHPK_wSJYNH2h4dCpB=
+You can reproduce this failure by adding this to your suite:
+
+  override val scalaCheckInitialSeed = "CTH6hXj8ViScMmsO78-k4_RytXHPK_wSJYNH2h4dCpB="
+
 ```
 
-To reproduce the exact same failure, you can override the test parameters and
-provide the offending seed as the initial seed:
+To reproduce the failure you can follow the suggestion to fix the seed:
 
 ```scala
-  override def scalaCheckTestParameters =
-    super.scalaCheckTestParameters.withInitialSeed(
-      "CTH6hXj8ViScMmsO78-k4_RytXHPK_wSJYNH2h4dCpB="
-    )
+class MySuite extends ScalaCheckSuite {
+
+  override val scalaCheckInitialSeed = "CTH6hXj8ViScMmsO78-k4_RytXHPK_wSJYNH2h4dCpB="
+
+  // ...
+}
 ```
 
 Re-running the test will now fail deterministically, which allows you to work on

diff --git a/munit-scalacheck/shared/src/main/scala/munit/ScalaCheckSuite.scala b/munit-scalacheck/shared/src/main/scala/munit/ScalaCheckSuite.scala
@@ -35,13 +35,7 @@ trait ScalaCheckSuite extends FunSuite {
 
   protected def scalaCheckPrettyParameters = Pretty.defaultParams
 
-  // Allow specifying an initial seed in its Base64 encoded form
-  implicit class XtensionScalaCheckTestParameters(
-      params: ScalaCheckTest.Parameters
-  ) {
-    def withInitialSeed(encodedSeed: String): ScalaCheckTest.Parameters =
-      params.withInitialSeed(Seed.fromBase64(encodedSeed).get)
-  }
+  protected def scalaCheckInitialSeed(): String = Seed.random().toBase64
 
   private val scalaCheckPropTransform: TestTransform =
     new TestTransform("ScalaCheck Prop", t => {
@@ -55,14 +49,21 @@ trait ScalaCheckSuite extends FunSuite {
 
   private def propToTry(prop: Prop, test: Test): Try[Unit] = {
     import ScalaCheckTest._
-    val seed = scalaCheckTestParameters.initialSeed.getOrElse(Seed.random())
+    val seed =
+      scalaCheckTestParameters.initialSeed.getOrElse(
+        Seed.fromBase64(scalaCheckInitialSeed()).get
+      )
     val result = check(scalaCheckTestParameters, prop.useSeed(test.name, seed))
     def renderResult(r: Result) = {
       val resultMessage = Pretty.pretty(r, scalaCheckPrettyParameters)
       if (r.passed) {
         resultMessage
       } else {
-        val seedMessage = s"Failing seed: ${seed.toBase64}\n"
+        val seedMessage = s"""|Failing seed: ${seed.toBase64}
+                              |You can reproduce this failure by adding this to your suite:
+                              |
+                              |  override val scalaCheckInitialSeed = "${seed.toBase64}"
+                              |""".stripMargin
         seedMessage + "\n" + resultMessage
       }
     }

diff --git a/tests/shared/src/main/scala/munit/ScalaCheckFrameworkSuite.scala b/tests/shared/src/main/scala/munit/ScalaCheckFrameworkSuite.scala
@@ -6,10 +6,8 @@ class ScalaCheckFrameworkSuite extends ScalaCheckSuite {
 
   // NOTE(gabro): this is needed for making the test output stable for the failed test below.
   // It also serves as a test for overriding these parameters.
-  override def scalaCheckTestParameters =
-    super.scalaCheckTestParameters.withInitialSeed(
-      "CTH6hXj8ViScMmsO78-k4_RytXHPK_wSJYNH2h4dCpB="
-    )
+  override val scalaCheckInitialSeed =
+    "CTH6hXj8ViScMmsO78-k4_RytXHPK_wSJYNH2h4dCpB="
 
   property("boolean check (true)") {
     forAll { (l1: List[Int], l2: List[Int]) =>
@@ -46,22 +44,25 @@ object ScalaCheckFrameworkSuite
     extends FrameworkTest(
       classOf[ScalaCheckFrameworkSuite],
       """|==> success munit.ScalaCheckFrameworkSuite.boolean check (true)
-         |==> failure munit.ScalaCheckFrameworkSuite.boolean check (false) - /scala/munit/ScalaCheckFrameworkSuite.scala:20
-         |19:
-         |20:  property("boolean check (false)") {
-         |21:    forAll { (n: Int) => scala.math.sqrt(n * n) == n }
+         |==> failure munit.ScalaCheckFrameworkSuite.boolean check (false) - /scala/munit/ScalaCheckFrameworkSuite.scala:18
+         |17:
+         |18:  property("boolean check (false)") {
+         |19:    forAll { (n: Int) => scala.math.sqrt(n * n) == n }
          |
          |Failing seed: CTH6hXj8ViScMmsO78-k4_RytXHPK_wSJYNH2h4dCpB=
+         |You can reproduce this failure by adding this to your suite:
+         |
+         |  override val scalaCheckInitialSeed = "CTH6hXj8ViScMmsO78-k4_RytXHPK_wSJYNH2h4dCpB="
          |
          |Falsified after 0 passed tests.
          |> ARG_0: -1
          |> ARG_0_ORIGINAL: 2147483647
          |==> success munit.ScalaCheckFrameworkSuite.tagged
          |==> success munit.ScalaCheckFrameworkSuite.assertions (true)
-         |==> failure munit.ScalaCheckFrameworkSuite.assertions (false) - /scala/munit/ScalaCheckFrameworkSuite.scala:38
-         |37:      assertEquals(n * 1, n)
-         |38:      assertEquals(n * n, n)
-         |39:      assertEquals(n + 0, n)
+         |==> failure munit.ScalaCheckFrameworkSuite.assertions (false) - /scala/munit/ScalaCheckFrameworkSuite.scala:36
+         |35:      assertEquals(n * 1, n)
+         |36:      assertEquals(n * n, n)
+         |37:      assertEquals(n + 0, n)
          |values are not the same
          |=> Obtained
          |1
@@ -70,6 +71,9 @@ object ScalaCheckFrameworkSuite
          |+-1
          |
          |Failing seed: CTH6hXj8ViScMmsO78-k4_RytXHPK_wSJYNH2h4dCpB=
+         |You can reproduce this failure by adding this to your suite:
+         |
+         |  override val scalaCheckInitialSeed = "CTH6hXj8ViScMmsO78-k4_RytXHPK_wSJYNH2h4dCpB="
          |
          |Falsified after 0 passed tests.
          |> ARG_0: -1