4 files changed, 42 insertions, 1 deletions
diff --git a/src/main/java/org/zwobble/mammoth/internal/docx/Relationships.java b/src/main/java/org/zwobble/mammoth/internal/docx/Relationships.java
index b1f2279..7e8c14c 100644
--- a/src/main/java/org/zwobble/mammoth/internal/docx/Relationships.java
+++ b/src/main/java/org/zwobble/mammoth/internal/docx/Relationships.java
@@ -15,6 +15,7 @@ public class Relationships {
     }
 
     public Relationship findRelationshipById(String id) {
-        return lookup(relationships, id).get();
+        return lookup(relationships, id)
+            .orElseThrow(() -> new RuntimeException("Could not find relationship '" + id + "'"));
     }
 }
diff --git a/src/test/java/org/zwobble/mammoth/tests/docx/RelationshipsTests.java b/src/test/java/org/zwobble/mammoth/tests/docx/RelationshipsTests.java
new file mode 100644
index 0000000..f9a7672
--- /dev/null
+++ b/src/test/java/org/zwobble/mammoth/tests/docx/RelationshipsTests.java
@@ -0,0 +1,19 @@
+package org.zwobble.mammoth.tests.docx;
+
+import org.junit.Test;
+import org.zwobble.mammoth.internal.docx.Relationships;
+
+import static org.junit.Assert.assertEquals;
+import static org.zwobble.mammoth.internal.util.MammothMaps.map;
+import static org.zwobble.mammoth.tests.util.MammothAsserts.assertThrows;
+
+public class RelationshipsTests {
+    @Test
+    public void exceptionIsThrownIfRelationshipCannotBeFound() {
+        Relationships relationships = new Relationships(map());
+        RuntimeException exception = assertThrows(
+            RuntimeException.class,
+            () -> relationships.findRelationshipById("rId5"));
+        assertEquals("Could not find relationship 'rId5'", exception.getMessage());
+    }
+}
diff --git a/src/test/java/org/zwobble/mammoth/tests/util/Action.java b/src/test/java/org/zwobble/mammoth/tests/util/Action.java
new file mode 100644
index 0000000..c99a770
--- /dev/null
+++ b/src/test/java/org/zwobble/mammoth/tests/util/Action.java
@@ -0,0 +1,6 @@
+package org.zwobble.mammoth.tests.util;
+
+@FunctionalInterface
+public interface Action {
+    void run();
+}
diff --git a/src/test/java/org/zwobble/mammoth/tests/util/MammothAsserts.java b/src/test/java/org/zwobble/mammoth/tests/util/MammothAsserts.java
new file mode 100644
index 0000000..2439ee2
--- /dev/null
+++ b/src/test/java/org/zwobble/mammoth/tests/util/MammothAsserts.java
@@ -0,0 +1,15 @@
+package org.zwobble.mammoth.tests.util;
+
+import org.zwobble.mammoth.internal.util.Casts;
+
+public class MammothAsserts {
+    public static <T extends Throwable> T assertThrows(Class<T> exceptionType, Action action) throws T {
+        try {
+            action.run();
+            throw new AssertionError("Expected exception");
+        } catch (RuntimeException exception) {
+            return Casts.tryCast(exceptionType, exception)
+                .orElseThrow(() -> exception);
+        }
+    }
+}