diff --git a/src/matchesAll.zig b/src/matchesAll.zig
index fefa2186f9fb3e4d2015ec7ac8ef12874ddfbc6d..673cd1b2f01defb711906e8f6f42a86881efe3aa 100644
--- a/src/matchesAll.zig
+++ b/src/matchesAll.zig
@@ -10,3 +10,21 @@ pub fn matchesAll(comptime T: type, haystack: []const T, comptime needle: fn (T)
     }
     return true;
 }
+
+const S = struct {
+    fn needle(item: u8) bool {
+        return item == 4;
+    }
+};
+test {
+    try std.testing.expect(matchesAll(u8, &.{ 4, 4, 4, 4, 4, 4 }, S.needle));
+}
+test {
+    try std.testing.expect(!matchesAll(u8, &.{ 4, 4, 4, 3, 4, 4 }, S.needle));
+}
+test {
+    try std.testing.expect(!matchesAll(u8, &.{ 0, 1, 2, 3, 4, 5 }, S.needle));
+}
+test {
+    try std.testing.expect(!matchesAll(u8, &.{ 5, 6, 7, 8, 9, 0 }, S.needle));
+}
diff --git a/src/matchesAny.zig b/src/matchesAny.zig
index 7935a4ca3be6778059245cd331cd1e7db68aec64..03bd4b2e7a40b295659f8ab591fffca6dbfb5176 100644
--- a/src/matchesAny.zig
+++ b/src/matchesAny.zig
@@ -10,3 +10,21 @@ pub fn matchesAny(comptime T: type, haystack: []const T, comptime needle: fn (T)
     }
     return false;
 }
+
+test {
+    const S = struct {
+        fn needle(item: u8) bool {
+            return item == 4;
+        }
+    };
+    try std.testing.expect(matchesAny(u8, &.{ 0, 1, 2, 3, 4, 5 }, S.needle));
+}
+
+test {
+    const S = struct {
+        fn needle(item: u8) bool {
+            return item == 7;
+        }
+    };
+    try std.testing.expect(!matchesAny(u8, &.{ 0, 1, 2, 3, 4, 5 }, S.needle));
+}
diff --git a/src/nullifyS.zig b/src/nullifyS.zig
index dac000a9cb3baeb66f053669e84cdea0f6c407f1..dba9f6ad04ce7bdab301eacebca1484cf7340ad8 100644
--- a/src/nullifyS.zig
+++ b/src/nullifyS.zig
@@ -7,3 +7,15 @@ pub fn nullifyS(s: ?string) ?string {
     if (s.?.len == 0) return null;
     return s.?;
 }
+
+test {
+    try std.testing.expect(nullifyS(null) == null);
+}
+test {
+    try std.testing.expect(nullifyS("") == null);
+}
+test {
+    try std.testing.expect(nullifyS("a") != null);
+    try std.testing.expect(nullifyS("a").?.len == 1);
+    try std.testing.expect(nullifyS("a").?[0] == 'a');
+}
diff --git a/src/opslice.zig b/src/opslice.zig
index 7580099aadb878d8b19269f69667cb81697d347f..8f46d11e2d6545e74c3fcccbe204dc688664532d 100644
--- a/src/opslice.zig
+++ b/src/opslice.zig
@@ -6,3 +6,16 @@ pub fn opslice(slice: anytype, index: usize) ?std.meta.Child(@TypeOf(slice)) {
     if (slice.len <= index) return null;
     return slice[index];
 }
+
+test {
+    const array = [_]u8{ 0, 1, 2, 3, 4, 5 };
+    const slice: []const u8 = &array;
+
+    try std.testing.expect(opslice(slice, 0) == 0);
+    try std.testing.expect(opslice(slice, 1) == 1);
+    try std.testing.expect(opslice(slice, 2) == 2);
+    try std.testing.expect(opslice(slice, 3) == 3);
+    try std.testing.expect(opslice(slice, 4) == 4);
+    try std.testing.expect(opslice(slice, 5) == 5);
+    try std.testing.expect(opslice(slice, 6) == null);
+}
diff --git a/src/sliceTo.zig b/src/sliceTo.zig
index eeaec8e7879745cfbadd0e66fa570a609b029f07..eae6203c9dcd5793fdbe4b3bed9cc77d2f8bef45 100644
--- a/src/sliceTo.zig
+++ b/src/sliceTo.zig
@@ -8,3 +8,13 @@ pub fn sliceTo(comptime T: type, haystack: []const T, needle: T) []const T {
     }
     return haystack;
 }
+
+test {
+    try std.testing.expect(std.mem.eql(u8, sliceTo(u8, "abcdefgh", 'd'), "abc"));
+}
+test {
+    try std.testing.expect(std.mem.eql(u8, sliceTo(u8, "abcdefgh", 'r'), "abcdefgh"));
+}
+test {
+    try std.testing.expect(std.mem.eql(u8, sliceTo(u8, "abcdefgh", 'a'), ""));
+}