diff --git a/.github/workflows/python-app.yml b/.github/workflows/python-app.yml
new file mode 100644
index 0000000..7820094
--- /dev/null
+++ b/.github/workflows/python-app.yml
@@ -0,0 +1,46 @@
+# This workflow will install Python dependencies, run tests and lint with a single version of Python
+# For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-python
+
+name: Python application
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Python 3.10
+      uses: actions/setup-python@v3
+      with:
+        python-version: "3.10"
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install flake8 pytest pytest-cov
+        if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+    - name: Lint with flake8
+      run: |
+        # stop the build if there are Python syntax errors or undefined names
+        flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+        # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
+        flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
+    - name: Test with pytest and calculate coverage
+      run: |
+        pytest --cov-report "xml:coverage.xml"  --cov=.
+    - name: Create Coverage
+      if: ${{ github.event_name == 'pull_request' }}
+      uses: orgoro/coverage@v3
+      with:
+          coverageFile: coverage.xml
+          token: ${{ secrets.GITHUB_TOKEN }}
diff --git a/__pycache__/functions.cpython-312.pyc b/__pycache__/functions.cpython-312.pyc
new file mode 100644
index 0000000..24a0e57
Binary files /dev/null and b/__pycache__/functions.cpython-312.pyc differ
diff --git a/__pycache__/test_functions.cpython-312-pytest-8.3.2.pyc b/__pycache__/test_functions.cpython-312-pytest-8.3.2.pyc
new file mode 100644
index 0000000..d073533
Binary files /dev/null and b/__pycache__/test_functions.cpython-312-pytest-8.3.2.pyc differ
diff --git a/functions.py b/functions.py
index 7cdbb28..a6481f0 100644
--- a/functions.py
+++ b/functions.py
@@ -3,7 +3,7 @@ def add(a, b):
 
 
 def subtract(a, b):
-    return a + b
+    return a - b
 
 
 def multiply(a, b):
@@ -11,4 +11,6 @@ def multiply(a, b):
 
 
 def convert_fahrenheit_to_celsius(fahrenheit):
-    return multiply(subtract(fahrenheit, 32), 9 / 5)
+    if fahrenheit < -459.67:
+        raise AssertionError("Temperature below absolute zero is not possible.")
+    return multiply(subtract(fahrenheit, 32), 5 / 9)
diff --git a/test_functions.py b/test_functions.py
index ffd7a65..cf4f2b9 100644
--- a/test_functions.py
+++ b/test_functions.py
@@ -8,12 +8,12 @@ def test_add():
     assert add("space", "ship") == "spaceship"
 
 
-# def test_subtract():
-#    assert subtract(3,2) == 1
+def test_subtract():
+    assert subtract(3,2) == 1
 
 
-# def test_convert_fahrenheit_to_celsius():
-#    assert f2c(32) == 0
-#    assert f2c(122) == pytest.approx(50)
-#    with pytest.raises(AssertionError):
-#        f2c(-600)
+def test_convert_fahrenheit_to_celsius():
+    assert f2c(32) == 0
+    assert f2c(122) == pytest.approx(50)
+    with pytest.raises(AssertionError):
+        f2c(-600)