add tests

Author: Jasper-M

compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTests.scala

@@ -1294,4 +1294,83 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       val JavaSymbolIsNotAValue(symbol) = messages.head
       assertEquals(symbol.show, "package p")
     }
+
+  @Test def userDefinedImplicitAmbiguous1 =
+    checkMessagesAfter("frontend") {
+      """
+        |object Test {
+        |  trait =!=[C, D]
+        |
+        |  implicit def neq[E, F] : E =!= F = null
+        |
+        |  @annotation.implicitAmbiguous("Could not prove ${J} =!= ${J}")
+        |  implicit def neqAmbig1[G, H, J] : J =!= J = null
+        |  implicit def neqAmbig2[I] : I =!= I = null
+        |
+        |  implicitly[Int =!= Int]
+          }
+
+      """.stripMargin
+    }.expect { (itcx, messages) =>
+      import diagnostic.NoExplanation
+      implicit val ctx: Context = itcx
+
+      assertMessageCount(1, messages)
+      val (m: NoExplanation) :: Nil = messages
+
+      assertEquals(m.msg, "Could not prove Int =!= Int")
+    }
+
+  @Test def userDefinedImplicitAmbiguous2 =
+    checkMessagesAfter("frontend") {
+      """
+        |object Test {
+        |  trait =!=[C, D]
+        |
+        |  implicit def neq[E, F] : E =!= F = null
+        |
+        |  implicit def neqAmbig1[G, H, J] : J =!= J = null
+        |  @annotation.implicitAmbiguous("Could not prove ${I} =!= ${I}")
+        |  implicit def neqAmbig2[I] : I =!= I = null
+        |
+        |  implicitly[Int =!= Int]
+          }
+
+      """.stripMargin
+    }.expect { (itcx, messages) =>
+      import diagnostic.NoExplanation
+      implicit val ctx: Context = itcx
+
+      assertMessageCount(1, messages)
+      val (m: NoExplanation) :: Nil = messages
+
+      assertEquals(m.msg, "Could not prove Int =!= Int")
+    }
+
+  @Test def userDefinedImplicitAmbiguous3 =
+    checkMessagesAfter("frontend") {
+      """
+        |object Test {
+        |  trait =!=[C, D]
+        |
+        |  implicit def neq[E, F] : E =!= F = null
+        |
+        |  @annotation.implicitAmbiguous("Could not prove ${J} =!= ${J}")
+        |  implicit def neqAmbig1[G, H, J] : J =!= J = null
+        |  @annotation.implicitAmbiguous("Could not prove ${I} =!= ${I}")
+        |  implicit def neqAmbig2[I] : I =!= I = null
+        |
+        |  implicitly[Int =!= Int]
+          }
+
+      """.stripMargin
+    }.expect { (itcx, messages) =>
+      import diagnostic.NoExplanation
+      implicit val ctx: Context = itcx
+
+      assertMessageCount(1, messages)
+      val (m: NoExplanation) :: Nil = messages
+
+      assertEquals(m.msg, "Could not prove Int =!= Int")
+    }
 }