diff --git a/analysis/dep_reg_dataset.py b/analysis/dep_reg_dataset.py
index 95bba39..94b8a36 100644
--- a/analysis/dep_reg_dataset.py
+++ b/analysis/dep_reg_dataset.py
@@ -55,8 +55,10 @@
 # Latest episode of depression is not followed by a depression resolved code.
 # Must be aged 18 or over on the achievement date
 
-dep1_reg_r1 = ((dataset.depr_dat.is_on_or_after(min_date))
-               & (dataset.depres_dat.is_null()))
+dep1_reg_r1 = (
+    (dataset.depr_dat.is_on_or_after(min_date)) & 
+    ( (dataset.depres_dat.is_null()) | (dataset.depres_dat < dataset.depr_dat) )
+    )
 dep2_reg_r2 = dataset.pat_age >= 18
 
-dataset.define_population(has_registration & dep1_reg_r1 & dep2_reg_r2)
+dataset.define_population(has_registration & dep1_reg_r1 &dep2_reg_r2)
diff --git a/analysis/test_dep_reg_dataset.py b/analysis/test_dep_reg_dataset.py
new file mode 100644
index 0000000..a14da6d
--- /dev/null
+++ b/analysis/test_dep_reg_dataset.py
@@ -0,0 +1,77 @@
+from datetime import date
+from dep_reg_dataset import dataset
+
+test_data = {
+    # Test rule 1: Patient excluded due to case before April 2006
+    1: {
+        "practice_registrations": [{
+            "start_date": date(2010, 1, 1),
+        }], 
+        "clinical_events": [{
+            "snomedct_code": "104851000119103",
+            "date": date(2005, 1, 1)
+        }],
+        "patients": {
+            "date_of_birth": date(1950, 1, 1)
+        },
+        "expected_in_population": False,
+    },
+    # Test rule 2: Patients excluded due to depression resolved code
+    # after depression incident case
+    2: {
+        "practice_registrations": [{
+            "start_date": date(1950, 1, 1)
+        }],
+        "clinical_events": [
+            {
+            "snomedct_code": "104851000119103",
+            "date": date(2009, 1, 1)},
+            {
+            "snomedct_code": "196381000000100",
+            "date": date(2010, 1, 1)
+        }],
+        "patients": {
+            "date_of_birth": date(1950, 1, 1)
+        },
+        "expected_in_population": False
+    },
+    # Test rule 3: Patients excluded due to being under 18
+    3: {
+        "practice_registrations": [{
+            "start_date": date(1950, 1, 1)
+        }],
+        "clinical_events": [
+            {
+            "snomedct_code": "104851000119103",
+            "date": date(2009, 1, 1)}],
+        "patients": {
+            "date_of_birth": date(2008, 1, 1)
+        },
+        "expected_in_population": False
+    },
+    # Patient who passess all rules
+    4: {
+        "practice_registrations": [{
+            "start_date": date(1950, 1, 1)
+        }],
+        "clinical_events": [
+            {
+            "snomedct_code": "104851000119103",
+            "date": date(2009, 1, 1)
+            },
+            {
+            "snomedct_code": "196381000000100",
+            "date": date(2008, 1, 1)
+            }
+        ], 
+        "patients": {
+            "date_of_birth": date(1990, 1, 1)
+        },
+        "expected_in_population": True,
+        "expected_columns": {
+            "pat_age": 34,
+            "depr_dat": date(2009, 1, 1),
+            "depres_dat": date(2008, 1, 1)
+        }
+    }
+}
\ No newline at end of file
diff --git a/project.yaml b/project.yaml
index daac3bb..edd0fb9 100644
--- a/project.yaml
+++ b/project.yaml
@@ -53,7 +53,9 @@ actions:
       highly_sensitive:
         measure: output/dep/dep_jaidip.csv.gz
   generate_dep_reg_dataset:
-    run: ehrql:v1 generate-dataset analysis/dep_reg_dataset.py --output output/dep/dep_reg_dataset.csv.gz
+    run: ehrql:v1 generate-dataset analysis/dep_reg_dataset.py 
+          --output output/dep/dep_reg_dataset.csv.gz
+          --test-data-file analysis/test_dep_reg_dataset.py
     outputs:
       highly_sensitive:
         dataset: output/dep/dep_reg_dataset.csv.gz