diff --git a/.travis.yml b/.travis.yml
index 7020efb78..0e7cefcf4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -12,6 +12,8 @@ jobs:
       osx_image: xcode9.4  # Python 3.7.4 running on macOS 10.14.4
       language: shell       # 'language: python' is an error on Travis CI macOS
       before_install:
+        - brew update-reset
+        - source ~/.bash_profile
         - brew update
         - brew install openslide
         - echo 'export PATH="/usr/local/Frameworks/Python.framework/Versions/Current/bin:$PATH"' >> /Users/travis/.bash_profile
diff --git a/src/histolab/data/__init__.py b/src/histolab/data/__init__.py
index a9b521413..b0f0d4fbc 100644
--- a/src/histolab/data/__init__.py
+++ b/src/histolab/data/__init__.py
@@ -240,7 +240,9 @@ def _load_svs(filename: str) -> Tuple[openslide.OpenSlide, str]:
 
 
 def aorta_tissue() -> Tuple[openslide.OpenSlide, str]:  # pragma: no cover
-    """Aorta tissue, brightfield, JPEG 2000, YCbCr
+    """aorta_tissue() -> Tuple[openslide.OpenSlide, str]
+
+    Aorta tissue, brightfield, JPEG 2000, YCbCr
 
     This image is available here
     http://openslide.cs.cmu.edu/download/openslide-testdata/Aperio/
@@ -258,7 +260,9 @@ def aorta_tissue() -> Tuple[openslide.OpenSlide, str]:  # pragma: no cover
 
 
 def breast_tissue() -> Tuple[openslide.OpenSlide, str]:  # pragma: no cover
-    """Breast tissue, TCGA-BRCA dataset.
+    """breast_tissue() -> Tuple[openslide.OpenSlide, str]
+
+    Breast tissue, TCGA-BRCA dataset.
 
     This image is available here
     https://portal.gdc.cancer.gov/files/9c960533-2e58-4e54-97b2-8454dfb4b8c8
@@ -280,7 +284,9 @@ def breast_tissue() -> Tuple[openslide.OpenSlide, str]:  # pragma: no cover
 def breast_tissue_diagnostic_green_pen() -> Tuple[
     openslide.OpenSlide, str
 ]:  # pragma: no cover
-    """Breast tissue, TCGA-BRCA dataset. Diagnostic slide with green pen.
+    """breast_tissue_diagnostic_green_pen() -> Tuple[openslide.OpenSlide, str]
+
+    Breast tissue, TCGA-BRCA dataset. Diagnostic slide with green pen.
 
     This image is available here
     https://portal.gdc.cancer.gov/files/da36d3aa-9b19-492a-af4f-cc028a926d96
@@ -302,7 +308,9 @@ def breast_tissue_diagnostic_green_pen() -> Tuple[
 def breast_tissue_diagnostic_red_pen() -> Tuple[
     openslide.OpenSlide, str
 ]:  # pragma: no cover
-    """Breast tissue, TCGA-BRCA dataset. Diagnostic slide with red pen.
+    """breast_tissue_diagnostic_red_pen() -> Tuple[openslide.OpenSlide, str]
+
+    Breast tissue, TCGA-BRCA dataset. Diagnostic slide with red pen.
 
     This image is available here
     https://portal.gdc.cancer.gov/files/f8b4cee6-9149-45b4-ae53-82b0547e1e34
@@ -324,7 +332,9 @@ def breast_tissue_diagnostic_red_pen() -> Tuple[
 def breast_tissue_diagnostic_black_pen() -> Tuple[
     openslide.OpenSlide, str
 ]:  # pragma: no cover
-    """Breast tissue, TCGA-BRCA dataset. Diagnostic slide with black pen.
+    """breast_tissue_diagnostic_black_pen() -> Tuple[openslide.OpenSlide, str]
+
+    Breast tissue, TCGA-BRCA dataset. Diagnostic slide with black pen.
 
     This image is available here
     https://portal.gdc.cancer.gov/files/31e248bf-ee24-4d18-bccb-47046fccb461
@@ -344,7 +354,9 @@ def breast_tissue_diagnostic_black_pen() -> Tuple[
 
 
 def cmu_small_region() -> Tuple[openslide.OpenSlide, str]:
-    """Carnegie Mellon University MRXS sample tissue
+    """cmu_small_region() -> Tuple[openslide.OpenSlide, str]
+
+    Carnegie Mellon University MRXS sample tissue
 
     This image is available here
     http://openslide.cs.cmu.edu/download/openslide-testdata/Aperio/
@@ -362,7 +374,9 @@ def cmu_small_region() -> Tuple[openslide.OpenSlide, str]:
 
 
 def heart_tissue() -> Tuple[openslide.OpenSlide, str]:  # pragma: no cover
-    """Heart tissue, brightfield, JPEG 2000, YCbCr
+    """heart_tissue() -> Tuple[openslide.OpenSlide, str]
+
+    Heart tissue, brightfield, JPEG 2000, YCbCr
 
     This image is available here
     http://openslide.cs.cmu.edu/download/openslide-testdata/Aperio/
@@ -380,7 +394,9 @@ def heart_tissue() -> Tuple[openslide.OpenSlide, str]:  # pragma: no cover
 
 
 def ovarian_tissue() -> Tuple[openslide.OpenSlide, str]:  # pragma: no cover
-    """Ovarian tissue, TCGA-OV dataset.
+    """ovarian_tissue() -> Tuple[openslide.OpenSlide, str]
+
+    Ovarian tissue, TCGA-OV dataset.
 
     This image is available here
     https://portal.gdc.cancer.gov/cases/b777ec99-2811-4aa4-9568-13f68e380c86
@@ -401,7 +417,9 @@ def ovarian_tissue() -> Tuple[openslide.OpenSlide, str]:  # pragma: no cover
 
 
 def prostate_tissue() -> Tuple[openslide.OpenSlide, str]:  # pragma: no cover
-    """Prostate tissue, TCGA-PRAD dataset.
+    """prostate_tissue() -> Tuple[openslide.OpenSlide, str]
+
+    Prostate tissue, TCGA-PRAD dataset.
 
     This image is available here
     https://portal.gdc.cancer.gov/files/6b725022-f1d5-4672-8c6c-de8140345210