diff --git a/wot-dijkstra/src/test/kotlin/org/pgpainless/wot/dijkstra/CertificationSetTest.kt b/wot-dijkstra/src/test/kotlin/org/pgpainless/wot/dijkstra/CertificationSetTest.kt
index 200cad65..be99c830 100644
--- a/wot-dijkstra/src/test/kotlin/org/pgpainless/wot/dijkstra/CertificationSetTest.kt
+++ b/wot-dijkstra/src/test/kotlin/org/pgpainless/wot/dijkstra/CertificationSetTest.kt
@@ -23,15 +23,15 @@ class CertificationSetTest {
     private val charlieSignsBob = Certification(charlie, null, bob, Date())
 
     @Test
-    fun emptyCertificationSet() {
+    fun `verify that properties of an empty CertificationSet are also empty`() {
         val empty = CertificationSet.empty(alice, bob)
-        assertTrue { empty.certifications.isEmpty() }
+        assert(empty.certifications.isEmpty())
         assertEquals(alice, empty.issuer)
         assertEquals(bob, empty.target)
     }
 
     @Test
-    fun addCertification() {
+    fun `verify that add()ing Certification objects works if issuer and target match that of the CertificationSet`() {
         val set = CertificationSet.empty(alice, bob)
 
         set.add(aliceSignsBob)
@@ -44,33 +44,63 @@ class CertificationSetTest {
         assertTrue {
             set.certifications["Bob <bob@example.org>"]!!.contains(aliceSignsBobUserId)
         }
+    }
 
+    @Test
+    fun `verify that add()ing another Certification object fails if the issuer mismatches`() {
+        val set = CertificationSet.empty(alice, bob)
         assertThrows<IllegalArgumentException> { set.add(charlieSignsBob) }
+    }
+
+    @Test
+    fun `verify that add()ing another Certification object fails if the target mismatches`() {
+        val set = CertificationSet.empty(alice, bob)
         assertThrows<IllegalArgumentException> { set.add(aliceSignsCharlie) }
     }
 
     @Test
-    fun mergeCertificationSets() {
+    fun `verify that merge()ing another CertificationSet works if issuer and target match that of the CertificationSet`() {
         val set = CertificationSet.fromCertification(aliceSignsBob)
         val others = CertificationSet.fromCertification(aliceSignsBobUserId)
-        val mismatch = CertificationSet.fromCertification(charlieSignsBob)
 
         set.merge(others)
         assertEquals(2, set.certifications.size)
         assertTrue { set.certifications[null]!!.contains(aliceSignsBob) }
         assertTrue { set.certifications["Bob <bob@example.org>"]!!.contains(aliceSignsBobUserId) }
-
-        assertThrows<IllegalArgumentException> { set.merge(mismatch) }
-
-        set.merge(set)
-        assertEquals(2, set.certifications.size)
     }
 
     @Test
-    fun testToString() {
+    fun `verify that merge()ing another CertificationSet with mismatched issuer fails`() {
+        val set = CertificationSet.fromCertification(aliceSignsBob)
+        val issuerMismatch = CertificationSet.fromCertification(charlieSignsBob)
+
+        assertThrows<IllegalArgumentException> { set.merge(issuerMismatch) }
+    }
+
+    @Test
+    fun `verify that merge()ing another CertificationSet with mismatched target fails`() {
+        val set = CertificationSet.fromCertification(aliceSignsBob)
+        val targetMismatch = CertificationSet.fromCertification(aliceSignsCharlie)
+
+        assertThrows<IllegalArgumentException> { set.merge(targetMismatch) }
+    }
+
+    @Test
+    fun `verify that merge()ing a CertificationSet with itself is idempotent`() {
+        val set = CertificationSet.fromCertification(aliceSignsBob)
+        assertEquals(1, set.certifications.size)
+        set.merge(set)
+        assertEquals(1, set.certifications.size)
+    }
+
+    @Test
+    fun `verify that toString() of an empty CertificationSet is the empty string`() {
         val empty = CertificationSet.empty(alice, bob)
         assertEquals("", empty.toString())
+    }
 
+    @Test
+    fun `verify that toString() of a CertificationSet with two Certifications matches our expectations`() {
         val twoCerts = CertificationSet.fromCertification(aliceSignsBob)
         twoCerts.add(aliceSignsBobUserId)