Improve hypothesis strategy

tests/hypothesis_strategies/kernels.py

@@ -9,17 +9,20 @@
 matern_kernels = st.builds(
     MaternKernel,
     nu=st.sampled_from((0.5, 1.5, 2.5)),
-    lengthscale_prior=st.one_of(st.none(), priors),
+    lengthscale_prior=priors,
+    lengthscale_prior_initial_value=st.floats(min_value=0, exclude_min=True),
 )
-"""A strategy that generates Matern kernels."""
+"""A strategy that generates matern kernels."""
 
-base_kernels = matern_kernels
+
+base_kernels = st.one_of([matern_kernels])
 """A strategy that generates base kernels to be used within more complex kernels."""
 
 scale_kernels = st.builds(
     ScaleKernel,
     base_kernel=base_kernels,
-    outputscale_prior=st.one_of(st.none(), priors),
+    outputscale_prior=priors,
+    outputscale_prior_initial_value=st.floats(min_value=0, exclude_min=True),
 )
 """A strategy that generates scale kernels."""