Allow only models with intercept in single-argument ftest

src/ftest.jl

@@ -53,8 +53,13 @@ F-statistic: 241.62 on 12 observations and 1 degrees of freedom, p-value: <1e-07
 ```
 """
 function ftest(mod::LinearModel)
+    if !hasintercept(mod)
+        Base.warn("ftest only works for models with an intercept")
+        return nothing
+    end
+
     rss = deviance(mod)
-    tss = hasintercept(mod) ? nulldeviance(mod) : sum(mod.rr.y .^ 2)
+    tss = nulldeviance(mod)
 
     n = Int(nobs(mod))
     p = dof(mod) - Int(hasintercept(mod)) - 1 # -1 for dispersion parameter

test/runtests.jl

@@ -653,7 +653,6 @@ end
     othermod = lm(@formula(Result~Other), d).model
     nullmod = lm(@formula(Result~1), d).model
     bothmod = lm(@formula(Result~Other+Treatment), d).model
-    emptymod = lm(zeros((length(d.Result), 1)), d.Result)
     nointerceptmod = lm(reshape(d.Treatment, :, 1), d.Result)
 
     ft1 = ftest(mod)
@@ -699,14 +698,7 @@ end
     end
 
     ft4 = ftest(nointerceptmod)
-    ft4base = ftest(emptymod, nointerceptmod)
-    @test ft4.nobs == ft4base.nobs
-    @test ft4.dof ≈ dof(nointerceptmod) - dof(emptymod)
-    @test ft4.fstat ≈ ft4base.fstat[2]
-    @test ft4.pval ≈ ft4base.pval[2]
-    @test sprint(show, ft4) == """
-        F-test against the null model:
-        F-statistic: 2703.38 on 12 observations and 1 degrees of freedom, p-value: <1e-13"""
+    @test ft4 == nothing
 end
 
 @testset "F test for model comparison" begin