Fix broken file and dir helpers on Windows

internal/assertions/assertions.go

@@ -975,6 +975,29 @@ func MapNotContainsValueEqual[M ~map[K]V, K comparable, V interfaces.EqualFunc[V
 	})
 }
 
+func FileExists(file string) (s string) {
+	info, err := os.Stat(file)
+	if errors.Is(err, fs.ErrNotExist) {
+		s = "expected file to exist\n"
+		s += bullet(" name: %s\n", file)
+		s += bullet("error: %s\n", err)
+		return
+	}
+	if err != nil {
+		s = "got an unexpected error\n"
+		s += bullet("name: %s\n", file)
+		s += bullet("error: %s\n", err)
+		return
+	}
+
+	if info.IsDir() {
+		s = "expected file but is a directory\n"
+		s += bullet("name: %s\n", file)
+		return
+	}
+	return
+}
+
 func FileExistsFS(system fs.FS, file string) (s string) {
 	info, err := fs.Stat(system, file)
 	if errors.Is(err, fs.ErrNotExist) {
@@ -983,8 +1006,13 @@ func FileExistsFS(system fs.FS, file string) (s string) {
 		s += bullet("error: %s\n", err)
 		return
 	}
+	if err != nil {
+		s = "got an unexpected error\n"
+		s += bullet("name: %s\n", file)
+		s += bullet("error: %s\n", err)
+		return
+	}
 
-	// other errors - file probably exists but cannot be read
 	if info.IsDir() {
 		s = "expected file but is a directory\n"
 		s += bullet("name: %s\n", file)
@@ -993,6 +1021,21 @@ func FileExistsFS(system fs.FS, file string) (s string) {
 	return
 }
 
+func FileNotExists(file string) (s string) {
+	_, err := os.Stat(file)
+	if err == nil {
+		s = "expected file to not exist\n"
+		s += bullet("name: %s\n", file)
+		return
+	}
+	if !errors.Is(err, fs.ErrNotExist) {
+		s = "expected not existing file but got different error\n"
+		s += bullet("error: %s\n", err)
+		return
+	}
+	return
+}
+
 func FileNotExistsFS(system fs.FS, file string) (s string) {
 	_, err := fs.Stat(system, file)
 	if err == nil {
@@ -1008,15 +1051,42 @@ func FileNotExistsFS(system fs.FS, file string) (s string) {
 	return
 }
 
+func DirExists(directory string) (s string) {
+	info, err := os.Stat(directory)
+	if errors.Is(err, fs.ErrNotExist) {
+		s = "expected directory to exist\n"
+		s += bullet(" name: %s\n", directory)
+		s += bullet("error: %s\n", err)
+		return
+	}
+	if err != nil {
+		s = "got an unexpected error\n"
+		s += bullet("name: %s\n", directory)
+		s += bullet("error: %s\n", err)
+		return
+	}
+	if !info.IsDir() {
+		s = "expected directory but is a file\n"
+		s += bullet("name: %s\n", directory)
+		return
+	}
+	return
+}
+
 func DirExistsFS(system fs.FS, directory string) (s string) {
 	info, err := fs.Stat(system, directory)
-	if os.IsNotExist(err) {
+	if errors.Is(err, fs.ErrNotExist) {
 		s = "expected directory to exist\n"
 		s += bullet(" name: %s\n", directory)
 		s += bullet("error: %s\n", err)
 		return
 	}
-	// other errors - directory probably exists but cannot be read
+	if err != nil {
+		s = "got an unexpected error\n"
+		s += bullet("name: %s\n", directory)
+		s += bullet("error: %s\n", err)
+		return
+	}
 	if !info.IsDir() {
 		s = "expected directory but is a file\n"
 		s += bullet("name: %s\n", directory)
@@ -1025,6 +1095,16 @@ func DirExistsFS(system fs.FS, directory string) (s string) {
 	return
 }
 
+func DirNotExists(directory string) (s string) {
+	_, err := os.Stat(directory)
+	if !errors.Is(err, fs.ErrNotExist) {
+		s = "expected directory to not exist\n"
+		s += bullet("name: %s\n", directory)
+		return
+	}
+	return
+}
+
 func DirNotExistsFS(system fs.FS, directory string) (s string) {
 	_, err := fs.Stat(system, directory)
 	if !errors.Is(err, fs.ErrNotExist) {
@@ -1077,6 +1157,25 @@ func DirModeFS(system fs.FS, path string, permissions fs.FileMode) (s string) {
 	return
 }
 
+func FileContains(file, content string) (s string) {
+	b, err := os.ReadFile(file)
+	if err != nil {
+		s = "expected to read file\n"
+		s += bullet(" name: %s\n", file)
+		s += bullet("error: %s\n", err)
+		return
+	}
+	actual := string(b)
+	if !strings.Contains(string(b), content) {
+		s = "expected file contents\n"
+		s += bullet("  name: %s\n", file)
+		s += bullet("wanted: %s\n", content)
+		s += bullet("actual: %s\n", actual)
+		return
+	}
+	return
+}
+
 func FileContainsFS(system fs.FS, file, content string) (s string) {
 	b, err := fs.ReadFile(system, file)
 	if err != nil {

invocations_test.go

@@ -54,6 +54,15 @@ func (it *internalTest) assert() {
 	}
 }
 
+func (it *internalTest) assertNot() {
+	if !it.helper {
+		it.t.Fatal("should be marked as helper")
+	}
+	if it.trigger {
+		it.t.Fatalf("condition expected not to trigger; it did\ngot message %q in output", it.capture)
+	}
+}
+
 func (it *internalTest) post() {
 	if !strings.Contains(it.capture, "PostScript |") {
 		it.t.Fatal("expected post-script output")