Add route for displaying current Git SHA

For:
#9

.ebextensions/git.config

@@ -0,0 +1,4 @@
+# Git is needed for the route that displays the current Git SHA.
+packages:
+  yum:
+    git: []

src/app.py

@@ -3,6 +3,9 @@
 Set up API routes.
 """
 
+# Built-in libraries:
+import subprocess
+
 # Third-party dependencies:
 from flask import Flask
 
@@ -12,4 +15,16 @@
 @app.route("/")
 def hello_world():
     """A cheeky hello world route."""
-    return {"message": "Look on my Affiliations Service, ye Mighty, and despair!"}
+    return "<p>Look on my Affiliations Service, ye Mighty, and despair!</p>"
+
+
+@app.route("/sha")
+def current_git_sha():
+    """Displays current Git SHA."""
+    command = ["git", "rev-parse", "HEAD"]
+    output = subprocess.run(command, check=False, capture_output=True).stdout.decode(
+        "utf-8"
+    )
+    # Strip newline character from the end of the string.
+    sha = output[0 : len(output) - 1]
+    return sha

src/app_test.py

@@ -14,6 +14,14 @@ def test_root():
     """Ensure our cheeky hello world route works."""
     response = CLIENT.get("/")
     assert response.status_code == 200
-    assert response.json == {
-        "message": "Look on my Affiliations Service, ye Mighty, and despair!"
-    }
+    assert (
+        response.text
+        == "<p>Look on my Affiliations Service, ye Mighty, and despair!</p>"
+    )
+
+
+def test_sha():
+    """Ensure we can get a SHA."""
+    response = CLIENT.get("/sha")
+    assert response.status_code == 200
+    assert len(response.text) == 40  # SHA-1 is 40 characters in length.