From 08f105af6b7ae8d723bdf6a3eab8a232c7e2504a Mon Sep 17 00:00:00 2001
From: JetSetIlly <stephen.t.illingworth@gmail.com>
Date: Sat, 30 Mar 2024 07:09:25 +0000
Subject: [PATCH] added ExpectImplements() function to test package

---
 gui/sdlimgui/win_rom_select.go | 1 -
 test/doc.go                    | 3 +++
 test/expected.go               | 8 ++++++++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/gui/sdlimgui/win_rom_select.go b/gui/sdlimgui/win_rom_select.go
index be450ed3..bd80bc48 100644
--- a/gui/sdlimgui/win_rom_select.go
+++ b/gui/sdlimgui/win_rom_select.go
@@ -47,7 +47,6 @@ type winSelectROM struct {
 
 	currPath string
 	entries  []os.DirEntry
-	err      error
 
 	selectedFile           string
 	selectedFileBase       string
diff --git a/test/doc.go b/test/doc.go
index 2cd4af0c..3db15acb 100644
--- a/test/doc.go
+++ b/test/doc.go
@@ -18,11 +18,14 @@
 //
 // The ExpectEquality() is the most basic and probably the most useful function.
 // It compares like-typed variables for equality and returns true if they match.
+// ExpectInequality() is the inverse function.
 //
 // The ExpectFailure() and ExpectSuccess() functions test for failure and
 // success. These two functions work with bool or error and special handling for
 // nil.
 //
+// ExpectImplements() tests whether an instance implements the specified type.
+//
 // The Writer type meanwhile, implements the io.Writer interface and should be
 // used to capture output. The Writer.Compare() function can then be used to
 // test for equality.
diff --git a/test/expected.go b/test/expected.go
index ef046516..200f032f 100644
--- a/test/expected.go
+++ b/test/expected.go
@@ -34,6 +34,14 @@ func ExpectInequality[T comparable](t *testing.T, value T, expectedValue T) {
 	}
 }
 
+// ExpectImplements tests whether an instance is an implementation of type T
+func ExpectImplements[T comparable](t *testing.T, instance any, implements T) {
+	t.Helper()
+	if _, ok := instance.(T); !ok {
+		t.Fatalf("implementation test of type %T failed: type %T does not implement %T", instance, instance, implements)
+	}
+}
+
 // ExpectFailure tests argument v for a failure condition suitable for it's
 // type. Types bool and error are treated thus:
 //