Merge pull request #195 from nevillelyh/neville/seed

Report accurate ScalaCheck seed on failing test
scalameta · Sep 9, 2020 · 0c4ff57 · 0c4ff57
2 parents 4dc7b16 + cfa00c5
commit 0c4ff57
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Showing 2 changed files with 33 additions and 4 deletions.
diff --git a/munit-scalacheck/shared/src/main/scala/munit/ScalaCheckSuite.scala b/munit-scalacheck/shared/src/main/scala/munit/ScalaCheckSuite.scala
@@ -49,23 +49,29 @@ trait ScalaCheckSuite extends FunSuite {
 
   private def propToTry(prop: Prop, test: Test): Try[Unit] = {
     import ScalaCheckTest._
-    def seed =
+    def makeSeed() =
       scalaCheckTestParameters.initialSeed.getOrElse(
         Seed.fromBase64(scalaCheckInitialSeed).get
       )
+    val initialSeed = makeSeed()
+    var seed: Seed = initialSeed
     val result = check(
       scalaCheckTestParameters,
-      Prop(genParams => prop(genParams.withInitialSeed(seed)))
+      Prop { genParams =>
+        val r = prop(genParams.withInitialSeed(seed))
+        seed = seed.next
+        r
+      }
     )
     def renderResult(r: Result): String = {
       val resultMessage = Pretty.pretty(r, scalaCheckPrettyParameters)
       if (r.passed) {
         resultMessage
       } else {
-        val seedMessage = s"""|Failing seed: ${seed.toBase64}
+        val seedMessage = s"""|Failing seed: ${initialSeed.toBase64}
                               |You can reproduce this failure by adding the following override to your suite:
                               |
-                              |  override val scalaCheckInitialSeed = "${seed.toBase64}"
+                              |  override val scalaCheckInitialSeed = "${initialSeed.toBase64}"
                               |""".stripMargin
         seedMessage + "\n" + resultMessage
       }

diff --git a/tests/shared/src/test/scala/munit/ScalaCheckInitialSeedSuite.scala b/tests/shared/src/test/scala/munit/ScalaCheckInitialSeedSuite.scala
@@ -0,0 +1,23 @@
+package munit
+
+import scala.collection.mutable
+import org.scalacheck.Prop.forAll
+
+final class ScalaCheckInitialSeedSuite extends ScalaCheckSuite {
+
+  // initial seed should be used for the first out of 100 `minSuccessfulTests` only
+  override val scalaCheckInitialSeed =
+    "9SohH7wEYXCdXK4b9yM2d6TKIN2jBFcBs4QBta-2yTD="
+  private val ints = mutable.Set.empty[Int]
+
+  property("generating int") {
+    forAll { (i: Int) =>
+      ints.add(i)
+      true
+    }
+  }
+
+  test("generated int are not all the same") {
+    assert(ints.size > 1)
+  }
+}