- Changed display_header in src/penn_chime/presentation.py so mitigation

  text for values of `Rt < 1` mention halving (vs doubling) and report a
  positive unit of time.
- Changed `tests/test_app.py` to add `test_mitigation_statement` to test `Rt`
  values `>= 1` are described as doubling and `< 1` is described as halving.

Fixes #155

Author: Eric Smyth

src/penn_chime/presentation.py

@@ -63,7 +63,7 @@ def display_header(st, p):
 **{r_naught:.2f}**.
 
 **Mitigation**: A **{relative_contact_rate:.0%}** reduction in social contact after the onset of the
-outbreak reduces the doubling time to **{doubling_time_t:.1f}** days, implying an effective $R_t$ of **${r_t:.2f}$**.
+outbreak **{impact_statement:s} {doubling_time_t:.1f}** days, implying an effective $R_t$ of **${r_t:.2f}$**.
 """.format(
             total_infections=p.infected,
             initial_infections=p.known_infected,
@@ -77,7 +77,8 @@ def display_header(st, p):
             doubling_time=p.doubling_time,
             relative_contact_rate=p.relative_contact_rate,
             r_t=p.r_t,
-            doubling_time_t=p.doubling_time_t,
+            doubling_time_t=abs(p.doubling_time_t),
+            impact_statement=("halves the infections every" if p.r_t < 1 else "reduces the doubling time to")
         )
     )
 

tests/test_app.py

@@ -71,6 +71,30 @@ def test_the_rest_of_header_shows_up():
     ), "The whole header should render"
 
 
+def test_mitigation_statement():
+    st.cleanup()
+    expected_doubling = "outbreak **reduces the doubling time to 7.8** days"
+    display_header(st, PARAM)
+    assert len((list(filter(lambda s: expected_doubling in s, st.render_store))))
+    st.cleanup()
+    expected_halving = "outbreak **halves the infections every 51.9** days"
+    halving_params = Parameters(
+        current_hospitalized=100,
+        doubling_time=6.0,
+        known_infected=5000,
+        market_share=0.05,
+        relative_contact_rate=0.7,
+        susceptible=500000,
+        hospitalized=RateLos(0.05, 7),
+        icu=RateLos(0.02, 9),
+        ventilated=RateLos(0.01, 10),
+        n_days=60,
+    )
+    display_header(st, halving_params)
+    assert len((list(filter(lambda s: expected_halving in s, st.render_store))))
+    st.cleanup()
+
+
 st.cleanup()