diff --git a/test/filter_spec.js b/test/filter_spec.js
index 74c8865..4d47e5c 100644
--- a/test/filter_spec.js
+++ b/test/filter_spec.js
@@ -14,4 +14,65 @@ describe("Filters", function () {
         expect(MultiIni.filters).not.to.be.undefined;
         expect(MultiIni.filters).not.to.be.null;
     });
+
+    describe("lowercase", function () {
+        it("is available", function () {
+            expect(MultiIni.filters.lowercase).to.be.defined;
+        });
+
+        it("string should be lowercase", function () {
+            expect(MultiIni.filters.lowercase('Test')).to.equal('test');
+        });
+
+        it("anything else then string will be returned unmodified", function () {
+            expect(MultiIni.filters.lowercase(false)).to.equal(false);
+        });
+    });
+
+    describe("uppercase", function () {
+        it("is available", function () {
+            expect(MultiIni.filters.uppercase).to.be.defined;
+        });
+
+        it("string should be uppercase", function () {
+            expect(MultiIni.filters.uppercase('Test')).to.equal('TEST');
+        });
+
+        it("anything else then string will be returned unmodified", function () {
+            expect(MultiIni.filters.uppercase(false)).to.equal(false);
+        });
+    });
+
+    describe("trim", function () {
+        it("is available", function () {
+            expect(MultiIni.filters.trim).to.be.defined;
+        });
+
+        it("string should be trimmed", function () {
+            expect(MultiIni.filters.trim(' Test ')).to.equal('Test');
+        });
+
+        it("anything else then string will be returned unmodified", function () {
+            expect(MultiIni.filters.trim(false)).to.equal(false);
+        });
+    });
+
+    describe("constants", function () {
+        it("is available", function () {
+            expect(MultiIni.filters.constants).to.be.defined;
+        });
+
+        it("string should have replaced constants", function () {
+            const options = {constants: {CONSTANT: 'replaced'}};
+
+            expect(MultiIni.filters.constants('"Test " CONSTANT', options)).to.equal('"Test replaced"');
+            expect(MultiIni.filters.constants('"Test " CONSTANT " Test"', options)).to.equal('"Test replaced Test"');
+            expect(MultiIni.filters.constants('CONSTANT " Test"', options)).to.equal('"replaced Test"');
+        });
+
+        it("anything else then string will be returned unmodified", function () {
+            expect(MultiIni.filters.constants(false)).to.equal(false);
+        });
+    });
+
 });