add test corresponding to #21

tests/testthat/test-glm.R

@@ -0,0 +1,37 @@
+# From issue #21
+
+test_that("gnmFit handles linear fit provided optimal starting values", {
+    Mean <- c(1237.1, 5605.55, 801.45, 2713.55, 570.4, 193.1, 97.2, 11.05,
+              202.5, 7031.75, 2679.6, 1252.55, 735.6, 4088.05, 9818.7, 4486.45,
+              3104.85, 1189.3, 217.6, 603.2, 28.45)
+    VC <- c(33696.08, 296681.045, 24842.205, 31777.205, 1705.28, 950.48,
+            2693.78, 244.205, 3026.42, 17578.125, 3.92, 8281.845, 1280.18,
+            76479.605, 4665.78, 130101.005, 0.125, 9800, 18355.28, 1152,
+            1618.805)
+    dat <- data.frame(Mean=Mean,VC=VC)
+    coeffs <- c(beta1 = 4792.94726157285, beta2 = 0.00366035757993686)
+
+    # gnm with linear terms (calls glm.fit)
+    fitglm <- gnm(VC ~ I(Mean^2) , family = Gamma(link = "identity"), 
+                  data = data.frame(dat), start=coeffs, trace=TRUE)
+
+    # gnm with equivalent "nonlin" term
+    powfun <- function(x)
+    {
+        list(
+            predictors=list(beta1 = 1, beta2 = 1),
+            variables=list(substitute(x)),
+            term=function(predictors,variables){
+                paste( predictors[1],"+",predictors[2],"*",variables[1],"^2")
+            }
+        )
+    }
+    class(powfun) <- "nonlin"
+    form <- VC ~ powfun(Mean)-1
+    fitgnm <- gnm(formula = form, family = Gamma(link = "identity"), 
+                  data = data.frame(dat), start=coeffs, trace=TRUE)
+
+    expect_equivalent(coeffs, fitgnm$coefficients)
+    # glm always does an extra iteration, even from previously converged fit
+    expect_equivalent(coef(fitglm), coef(fitgnm), tolerance = 1e-6)
+})