From f8032b4304db5ccf71a3de1e5280bc22231cd3c5 Mon Sep 17 00:00:00 2001
From: James Harris <mailjamesharris@gmail.com>
Date: Wed, 15 Apr 2020 14:41:11 +1000
Subject: [PATCH] Implement `PanicWith()`.

---
 matchers.go                    | 10 ++++++++
 matchers/panic_matcher.go      | 44 ++++++++++++++++++++++++++++++---
 matchers/panic_matcher_test.go | 45 +++++++++++++++++++++++++++++++++-
 3 files changed, 94 insertions(+), 5 deletions(-)

diff --git a/matchers.go b/matchers.go
index cdf1476d6..16218d4c5 100644
--- a/matchers.go
+++ b/matchers.go
@@ -390,6 +390,16 @@ func Panic() types.GomegaMatcher {
 	return &matchers.PanicMatcher{}
 }
 
+//PanicWith succeeds if actual is a function that, when invoked, panics with a specific value.
+//Actual must be a function that takes no arguments and returns no results.
+//
+//By default PanicWith uses Equal() to perform the match, however a
+//matcher can be passed in instead:
+//    Expect(fn).Should(PanicWith(MatchRegexp(`.+Foo$`)))
+func PanicWith(expected interface{}) types.GomegaMatcher {
+	return &matchers.PanicMatcher{Expected: expected}
+}
+
 //BeAnExistingFile succeeds if a file exists.
 //Actual must be a string representing the abs path to the file being checked.
 func BeAnExistingFile() types.GomegaMatcher {
diff --git a/matchers/panic_matcher.go b/matchers/panic_matcher.go
index 640f4db1a..002ba75f7 100644
--- a/matchers/panic_matcher.go
+++ b/matchers/panic_matcher.go
@@ -8,7 +8,8 @@ import (
 )
 
 type PanicMatcher struct {
-	object interface{}
+	Expected interface{}
+	object   interface{}
 }
 
 func (matcher *PanicMatcher) Match(actual interface{}) (success bool, err error) {
@@ -28,7 +29,21 @@ func (matcher *PanicMatcher) Match(actual interface{}) (success bool, err error)
 	defer func() {
 		if e := recover(); e != nil {
 			matcher.object = e
-			success = true
+
+			if matcher.Expected == nil {
+				success = true
+				return
+			}
+
+			valueMatcher, valueIsMatcher := matcher.Expected.(omegaMatcher)
+			if !valueIsMatcher {
+				valueMatcher = &EqualMatcher{Expected: matcher.Expected}
+			}
+
+			success, err = valueMatcher.Match(e)
+			if err != nil {
+				err = fmt.Errorf("PanicMatcher's value matcher failed with:\n%s%s", format.Indent, err.Error())
+			}
 		}
 	}()
 
@@ -38,9 +53,30 @@ func (matcher *PanicMatcher) Match(actual interface{}) (success bool, err error)
 }
 
 func (matcher *PanicMatcher) FailureMessage(actual interface{}) (message string) {
-	return format.Message(actual, "to panic")
+	switch matcher.Expected.(type) {
+	case nil:
+		return format.Message(actual, "to panic")
+	case omegaMatcher:
+		return format.Message(actual, "to panic with a value matching", matcher.Expected)
+	default:
+		return format.Message(actual, "to panic with", matcher.Expected)
+	}
 }
 
 func (matcher *PanicMatcher) NegatedFailureMessage(actual interface{}) (message string) {
-	return format.Message(actual, fmt.Sprintf("not to panic, but panicked with\n%s", format.Object(matcher.object, 1)))
+	switch matcher.Expected.(type) {
+	case nil:
+		return format.Message(actual, fmt.Sprintf("not to panic, but panicked with\n%s", format.Object(matcher.object, 1)))
+	case omegaMatcher:
+		return format.Message(
+			actual,
+			fmt.Sprintf(
+				"not to panic with a value matching\n%s\nbut panicked with\n%s",
+				format.Object(matcher.Expected, 1),
+				format.Object(matcher.object, 1),
+			),
+		)
+	default:
+		return format.Message(actual, "not to panic with", matcher.Expected)
+	}
 }
diff --git a/matchers/panic_matcher_test.go b/matchers/panic_matcher_test.go
index 899fc108a..904b229bf 100644
--- a/matchers/panic_matcher_test.go
+++ b/matchers/panic_matcher_test.go
@@ -35,7 +35,7 @@ var _ = Describe("Panic", func() {
 	})
 
 	When("assertion fails", func() {
-		It("prints the object passed to Panic when negative", func() {
+		It("prints the object passed to panic() when negative", func() {
 			failuresMessages := InterceptGomegaFailures(func() {
 				Expect(func() { panic("ack!") }).NotTo(Panic())
 			})
@@ -50,3 +50,46 @@ var _ = Describe("Panic", func() {
 		})
 	})
 })
+
+var _ = Describe("PanicWith", func() {
+	When("passed a function of the correct type", func() {
+		It("should call the function and pass if the function panics with the expected value", func() {
+			Expect(func() { panic("ack!") }).To(PanicWith("ack!"))
+			Expect(func() {}).NotTo(PanicWith("ack!"))
+		})
+	})
+
+	When("assertion fails", func() {
+		It("prints simple message when positive", func() {
+			failuresMessages := InterceptGomegaFailures(func() {
+				Expect(func() {}).To(PanicWith("ack!"))
+			})
+			Expect(failuresMessages).To(ConsistOf(MatchRegexp("Expected\n\\s+<func\\(\\)>: .+\nto panic with\\s+<string>: ack!")))
+		})
+
+		It("prints simple message when negative", func() {
+			failuresMessages := InterceptGomegaFailures(func() {
+				Expect(func() { panic("ack!") }).NotTo(PanicWith("ack!"))
+			})
+			Expect(failuresMessages).To(ConsistOf(MatchRegexp("Expected\n\\s+<func\\(\\)>: .+\nnot to panic with\\s+<string>: ack!")))
+		})
+
+		When("the expected value is actually a matcher", func() {
+			It("prints simple message when positive", func() {
+				failuresMessages := InterceptGomegaFailures(func() {
+					Expect(func() {}).To(PanicWith(Equal("ack!")))
+				})
+				Expect(failuresMessages).To(ConsistOf(MatchRegexp("Expected\n\\s+<func\\(\\)>: .+\nto panic with a value matching\n.+EqualMatcher.+ack!")))
+			})
+
+			It("prints the object passed to panic() when negative", func() {
+				failuresMessages := InterceptGomegaFailures(func() {
+					Expect(func() { panic("ack!") }).NotTo(PanicWith(MatchRegexp("ack")))
+				})
+				Expect(failuresMessages).To(ConsistOf(
+					MatchRegexp("Expected\n\\s+<func\\(\\)>: .+\nnot to panic with a value matching\n.+MatchRegexpMatcher.+ack.+\nbut panicked with\n    <string>: ack!"),
+				))
+			})
+		})
+	})
+})